Root Crops in July

 

 

A fine rutabaga (Swede)!
Photo Produce Market Guide

Root Crops in July

Root Crops to Plant in Central Virginia in July

July is not a good month for sowing many root crops in Virginia – it’s hot and for most fall root crops we can do better waiting till August. Yes, it will still be hot in August, but the daylight is getting shorter and so the hot part of the day is also getting shorter. 

Carrots: if we really need more carrots, we direct sow our eighth bed of carrots in early July. We only do this if they’re really needed, because carrots grown in hot weather do not have the best flavor. They will not be sweet, they may even be bitter.  Our plan is to have grown enough between February and May to last us until late October, stored in perforated plastic bags in the walk-in cooler. But if earlier sowings weren’t all successful, or we ate unusually large amounts of carrots, we can find ourselves sowing them in July.

Use shadecloth to keep the soil damp, or water a lot. Carrot seed will germinate whenever the soil is below 95°F (35°C), provided you can keep the soil damp until the seedlings emerge. You won’t need to do daily watering for long: maybe only 4 days. We flame summer carrots on day 4 after sowing, because we have found that carrots can emerge on day 5 in summer temperatures, despite longer times given in the charts. See Root Crops in May for more about sowing and growing carrots, including pre-emergence flame weeding.

Young kohlrabi plants.
Photo Kathryn Simmons

Kohlrabi: Kohlrabi transplants successfully, unlike carrots and turnips, and this has usually been our method for fall crops. We have sown kohlrabi (Early Purple Vienna and Early White Vienna) in the week beginning July 2, for transplanting 8/3-8/9. Sowing in early August is also possible, for November harvests. Kohlrabi, like other brassicas, can be grown in spring or fall in our zone 7 climate. It’s not actually a root crop, rather a swollen stem, but I’m including it as an “acting root”

Rutabagas: This year we are growing rutabagas (also known as Swedes) again, after several years when we went with more turnips instead. Rutabagas are only sown here in late summer for winter storage. They take longer to grow to a good size than turnips do, so it is necessary to start earlier: 7/15-8/4 here, (mid-August at the latest), allowing 90-100 growing days before a hard freeze. Fall root crops sown too early in the summer can get woody. See the Special Topic for July below for all the details about rutabagas.

Root Crops to Harvest in Central Virginia in July

Potatoes: From mid-June onwards, we can harvest spring-planted potatoes as delicious “new” potatoes. See Root Crops in June for more on this. For maximum yields, hold off on harvesting until two weeks after tops have died. See next week’s post for all the details.

This garden worker loves washing beets!
Photo Wren Vile

Beets: We like to clear all our spring beets by the end of June, but sometimes the job flows over into July. Trimmed beets keep well in perforated plastic bags under refrigeration. Store beets at 32°F (0°C) and 95% humidity.

Carrots: Our third carrots (sown mid-March) should be cleared in early July if not before, and our fourth carrots (sown in late March) and fifth (sown in mid-April) will also be ready to harvest in July. I usually reckon on three months from sowing to harvest for carrots, but they can be faster in warm weather. Don’t leave them in the ground too long, or they will get woody. See Root Crops in June for more on carrots.

Kohlrabi: As with beets, we plan to harvest spring kohlrabi by the end of June, at 3” (7.5 cm) in diameter (or even up to softball size). They get too fibrous if left longer, so we will prioritize getting them up. The base of the globe can be tough, so cut either the wiry root just below the soil surface, or cut higher, leaving a small disc of the globe behind, attached to the taproot.

Turnips:  If we didn’t finish harvesting our spring turnips by the end of June, we really need to get them all up in early July. If we have more than we can eat in the next week, we store them in perforated plastic bags in the walk-in cooler, eating them during the summer. Turnips keep for about 4 months at temperatures close to freezing and humidity of 90-95%. Higher humidity will make them rot (rotting turnips are pretty unpleasant!)

Harvested Purple Top Milan and White Egg turnips.
Photo Pam Dawling

Other Root Crop Tasks in Central Virginia in July:

After all the spring-sown root crops are harvested, and the spring-sown greens have bolted, we prepare the emptied beds for summer or fall crops.

Preparing space for summer-planted crops

In July, we will be looking for beds to plant successions of lettuce, cucumbers, squash and beans; our fall brassica transplants, and our first transplants of fall and winter cabbage and Asian greens. In August, we’ll want beds for our last plantings of cucumbers, squash and beans, the never-ending lettuces, fall beets, turnips, winter radishes, kale, and collards. Harvesting the spring roots promptly and storing them gives us time to prepare the beds for their next crop.

Buckwheat cover crop in flower.
Photo Pam Dawling

Buckwheat

If we have 4 weeks or more before the next crop, we will sow a cover crop of buckwheat in the just-emptied beds. Buckwheat keeps the weeds down and feeds the soil (and the honeybees and other pollinating insects). If there are weeds or lots of crop debris, we will till deep enough to bury that plant matter, then broadcast the buckwheat at a rate of 2–4 oz/100 ft2 (6–12 gm/m2), give another shallow tilling, then water and stand back. If there are no weeds or crop debris, there’s no need to till: you can broadcast the seed, and rake it in before watering (and standing back!). As an alternative to broadcasting you can sow rows of buckwheat with the #22 plate on an EarthWay seeder.

Prepare stale seed beds for fall carrots

If you have less than four weeks before you need to sow or transplant the next crop, you can use the time to kill weeds with the stale seedbed technique. Prepare the bed as if you were about to sow, producing an even surface with a fine tilth (surface texture). Then water as if you had sown something, keeping the surface damp by watering as needed. As soon as you see tiny weeds germinating, hoe the surface very shallowly in sunny breezy weather and let the weeds dry out. Make a last hoeing the day before sowing the next crop. This is especially useful for carrots, scallions or anything with tiny seedlings, which cannot easily compete with weeds.

Another method of germinating and killing weed seedlings when there is no crop in the ground is tarping: cover the bed with an opaque waterproof cover after watering the soil. Weeds seeds germinate, but the weeds cannot grow without light and will die.

Solarizing with clear plastic. Photo Pam Dawling

Solarizing is another approach that works well in hot weather: cover the prepared bed with clear agricultural plastic, such as scraps of a hoophouse covering. The heat of the sun bakes any weed seeds near the surface, and also any disease spores or small pests. Larger creatures such as earthworms can burrow deeper into the soil (as they do anyway in hot weather).

Rutabagas, although these ones don’t have much in the way of necks, a usual distinguishing feature.
Photo Penn State

Special Root Crop Topic for July in Central Virginia: Rutabagas

Rutabagas need to be sown in July in central Virginia. To clarify: rutabagas (known as Swedes in the UK) are Brassica napus, closely related to most other brassica crops. Botanically, rutabagas are part swollen tap roots, part swollen stem (the upper portion of the vegetable which forms the neck, the distinguishing feature of rutabagas). There are secondary roots growing in two rows down the sides of rutabagas. Rutabagas are mostly yellow-fleshed with a tan and reddish or purplish skin, although there are white-fleshed varieties. They all have blue-green waxy, non-hairy leaves. turnips are Brassica rapa, like Chinese cabbage and mustards. Turnips come in a range of colors, white or yellow flesh, with white, purple, red or golden yellow skins. The leaves are bright grass green, usually hairy, and not waxy. Turnips do not have a neck or secondary roots growing off the turnip. Rutabagas have twice the nutrients of turnips. And take longer to grow.

Rutabagas are among the hardiest of vegetables, and can be left growing (or at least not dying) until all other crops have been harvested. The flavor improves after frost. For small plantings, plan on 10’ (3 m) per person. Yields of rutabagas can be 75-180 lbs of roots/100’, (35-80 kg roots/30 m): 50% higher than turnips.

Rutabagas come in very few varieties. Laurentian (95 days OP) has a deep purple crown and cream yellow bottom. The uniform 5–6″ (13-15 cm) roots have sweet pale yellow flesh. Joan (90 days, OP), looks similar to Laurentian, with the added advantage that it is somewhat tolerant to club root. Gilfeather (85 days, OP) is sold as a turnip, but is botanically a white rutabaga. Sweeter and later to mature than turnips, it doesn’t become woody even at softball size. Southern Exposure Seed Exchange also has American Purple Top (not to be confused with the Purple Top White Globe turnip) and the Lithuanian Nadmorska a large oval 90d OP.

Fine rows of rutabagas. See the distinctive necks.
Photo Nan Chase

Keys to growing mild, sweet-tasting rutabagas include cool temperatures, sufficient irrigation, and no competition from weeds or over-crowding. The optimal germination range is 59-95°F (15-35°C). Rutabagas are a little slower to germinate. We sow four rows in 4’ (1.2 m) wide beds. Seeds need to be 0.5” (1.2 cm) deep. When flea beetles or grasshoppers are a problem, use rowcover or insect mesh.

Early thinning is especially important for shapely well-developed rutabagas. Thin to 4” (10 cm) within 10 days of emergence, or at least by 1” (2.5 cm) tall, then to 10” (25 cm) when 2-3” (5-7.5 cm) tall. If not well-thinned, they will grow in odd shapes and be small. 

Boron deficiency causes the middles of the roots to turn brown. Many common weeds are in the Brassica family, and could harbor pests and diseases that could attack the crop, so use crop rotations, stale seedbeds and clean cultivation to remove the weeds.

Aphids, flea beetles, cabbage worms, harlequin bugs, and grasshoppers can all be a problem. Rutabagas have worse trouble with aphids than turnips. Brassica flea beetles are not the same species as the nightshade flea beetles often found on eggplant. Rowcovers or insect netting and the planting of insectaries (flowers to attract beneficial insects such as ladybugs) can help avoid the problems. Bt can be used for the caterpillars, soaps for the aphids and Nolo bait for the grasshoppers (except where banned in order to preserve rare species of grasshopper).

More information 

GrowVeg Rutabaga Growing Guide 

Written in Vermont: Gardener’s Path:

Written in Mother Earth News by Sara Pacher:

DIY Network

The main diseases of rutabagas (and turnips) are club-root, downy mildew, powdery mildew, rhizoctonia rot, bacterial scab, and blackleg. All except scab are fungal diseases. Organic methods of prevention are crop rotations and field sanitation (plowing in residues promptly, removing weeds). Club-root fungus is able to live in the soil for up to 10 years, so is hard to eliminate. Avoid all brassica crops in an affected field for 10 years, and be vigilant about eliminating brassica family weeds. (Develop a fondness for spinach, chard and beet greens!)

Our rutabagas are ready from mid-October. Rutabagas (but not turnips except in warm climates) can be stored in the ground all winter. Mulch over them with loose straw once the temperatures descend near 20°F (-7°C). If you don’t manage to eat all the roots before spring, they will re-sprout and you can have an “early spring bite” of greens (a term more usually used for cattle fodder crops).

Rutabagas can store for as much as 6 months in perforated plastic bags under refrigeration. They do best stored above 95% humidity. Prompt washing before the soil dries on the roots will make them easier to clean later.

In the UK, rutabagas are not waxed as they are in North America. In fact, they store well without waxing, and I encourage you to try skipping the petroleum product.

Sliced rutabaga.
Photo Cornell

Growing High-Yielding Sweet Potatoes

Healthy sweet potato plants. A few insect bites won’t hurt!
Photo Kathryn Simmons

Growing High-Yielding Sweet Potatoes

In May I gave information on planting sweet potatoes. Hopefully that went well for you, and by now you have a large patch of healthy green vines. Let’s keep it that way! Here I will tell you about what the growing plants need, and the pests, disease and afflictions to avoid.

Read more

I have a Sweet Potato slideshow. I have lot of other posts on sweet potatoes (mostly about propagating our own slips, or about harvesting). Click to see the links in last month’s post

The ATTRA publication Sweetpotato: Organic Production is a good introduction.

Oklahoma State University Extension Sweet Potato Production is a clear concise publication (although it’s not organic).

Sweet potato development

This paragraph was included in Planting Sweet Potatoes, and I’m repeating it here, as a good reality check on what you can expect.

Regardless of how early in the season you plant them out, they will not make flowers earlier, or start making tubers sooner. Both flower and tuber initiation are triggered by day length. Each variety has its own internal clock. Most varieties take 90–110 days from planting out to reach a good size, if the weather is warm enough.

The first month or so after transplanting is the root development stage. Roots can go 8’ (2.4 m) deep in 40 days. Don’t be alarmed at the lack of above-ground action. The second month or so is the vine growth stage. The roots begin to store starch and sugar close to the stem base. During the last month of growth for that variety (3rd or 4th month), the potatoes develop. Make sure you dig them up before the soil temperature gets down to 55˚F (13˚C) – the week of the average first fall frost is about right.

Growing sweet potatoes – Three Ws: water, warmth, weed-free
  1. Water
  • The critical time to maintain sufficient moisture is after transplanting for at least the first 20-40 days while roots are developing. By now, most growers will be beyond this most-important watering period. But if it’s less than 40 days since you planted them out, keep the soil moist. Use your fingers to test the soil for dampness.
  • Once they are established, sweet potato plants are fairly drought-tolerant. But if you want high yields, they’ll need water once a week, either from the sky, or provided by you. Note that if you are using plastic mulch, rain won’t go through it, so I hope you installed drip irrigation below the plastic. If not, lay it on top, right beside the plants. Aim to provide an inch (2.5 cm) of water per week.
  1. Warmth
  • Sweet potatoes need warmth! Heat determines success; the number of days from planting does not.
  • Provided the weather is warm enough, most varieties take 90–110 days from planting out to reach a good size.
  • You can gain warmth in a cold climate, by planting inside a hoophouse or low tunnel covered in clear plastic. Ventilate in hot weather.
  • Growing Degree Days (heat units) are a tool for measuring accumulated heat, but you don’t need to calculate GDDs to get a good crop!
  • Early varieties take 1200 GDDs to grow a good crop.
  • To calculate GDDs, take the day’s high temperature (max) and the day’s low temperature (min) and add them together. Divide by 2 and subtract the base temperature of 55F. (Apologies to the rest of the world – I only know this method using Fahrenheit, but I’m sure you can find out how to do the calculations in Celsius). There are phone apps that will do the calculation for you.
  • Example: For a daytime max of 90F, and a night-time min of 70F, you get 25 GDDs – just about perfect for sweet potatoes. 90+70=160. 160/2=80. 80-55=25. At 25 GDDs a day, you theoretically only need about 48 days to get a crop. There are some other limits to daily plant growth – the likely minimum for a decent crop is about 76 days.
  • In a plastic tunnel, you can get 20 GDDs a day or more, rather than the 5 you might get outdoors.

    Water, warmth and no weeds – all that growing sweet potatoes need.
    Photo Nina Gentle
  1. Weed-free
  • Cultivate to remove weeds until the vines cover the ground, after which very little weeding will be needed.
  • If you have plastic mulch, walk through pulling weeds, and drop them on the plastic to cook. If you are growing on bare soil, hoe while the weeds are small, and pull if the weeds and the vines get ahead of you.
  • Weeding is generally not onerous because the sweet potato vines cover the ground within 6 weeks of planting and smother any newly emerging weeds.
Our motion sensor sprinkler and the outer layer of our fence around the sweet potato patch at the end of May.
Photo Pam Dawling
Solar electric fence controller for our sweet potato patch.
Photo Wren Vile
Pest mammals
  • Deer eat sweet potato plants at all stages, including digging out the roots in the fall. Dogs, fences and guns are the three most effective methods of deer control. The plants can be covered with row cover or plastic net for the growing season. Motion-sensor sprayers work well if maintained.
  • Rabbits eat the foliage. Plant the slips on black plastic to hold back weeds, then put wire hoops over the rows and cover with row cover for 3–4 weeks while the plants are young. Even after the plants are large rabbits can cause substantial losses.
  • Groundhogs dig and eat the roots. They can be trapped with baits of fruit. What’s for dinner?
  • Pocket Gophers search out sweet potatoes to eat. Their mounds may be hidden under the foliage and the plants may survive as they only eat the larger roots, leaving no crop.
  • Voles move in from grassy areas to live under the mulch and feed as fast as the roots form. They eat the roots from the top down leaving the outer shell in the soil where they have feasted. Cats are the best control.
  • Rats love the roots. Cats or dogs are the best methods of control.
  • Field Mice build nests under black plastic and eat the roots emerging from the ground.
Why not eat some sweet potato leaves as summer greens?
Photo Nina Gentle
Human “pests” of sweet potatoes

 You can eat sweet potato leaves yourself and it takes several meals to reduce yields of the tubers. Some researchers working in Vietnam, discovered that harvesting 25%, 50%, 75% or 100% of the vines every 15, 20, or 30 days (ignoring the information about the season of the year and the varieties) gave the sort of results you might expect. Harvesting tops every 20 days gave highest yields of greens. Harvesting 50% of the greens each time gave highest total yields of greens. Harvesting not more than 25% or 50% of the greens each time gave the highest eventual tuber yields, after 120 days. Researchers in Tanzania came up with the clear information that harvesting three times at one month intervals gave the highest greens production, but the tuber yield was affected tremendously. Harvesting tops twice in a growing period proved the best in leaf production as well as root yields. So, clip 25-50% of the tops of each plant up to twice in one summer, and you’ll still get a good yield of roots.

Also see the University of Arkansas Extension Nutritional and Medicinal Qualities of Sweetpotato Tops and Leaves. This publication explains how to plant slips 2” (5 cm) apart, specifically for greens (vine tips) and harvest 6 times between the end of April and the end of October.

 Insect pests of sweet potatoes

See North Carolina State University, Pests of Sweetpotato  for photos, drawings and details.

Although there are many insect pests that feed on sweet potato vines and leaves, most do very little damage, and hunting them down is not justified.

Healthy sweet potato patch, with some deer nibbling and weeds..
Photo Wren Vile
Pests that feed on foliage
  • Sweet potato flea beetles – Tiny black/bronze oval beetles (1.6 mm long), with reddish-yellow legs, and ridged wing covers; make small shot-holes in leaves or grooves in the upper surface of the leaves. Damaged areas turn brown and die. See below about larvae.
  • Sweet potato weevil adults and larvae do feed on the foliage, but mostly go for the roots (see below).
  • Caterpillars of three kinds:
    • Southern armyworms – Gray-black larvae up to 36 mm long with green or pink tints; pale longitudinal stripes and pairs of triangular spots along the back; pale yellow heads with bright red-brown marks. They feed on leaves and tips of vines, and congregate around the bases of plants during the middle of the day.
    • Sweet potato hornworms – First instar: white with a black horn; later instars (up to 90 mm long): green or brown with black diagonal lines down each side and a black horn, with a green or brown head with black stripes. They defoliate plants and often hide under leaves near the bases of plants.
    • Yellow-striped armyworms – Pale gray-black caterpillars up to 45 mm long, with orange-yellow stripes along the sides and pairs of triangular spots on the back of most segments; brown heads with black markings and a white inverted V. They feed similarly to southern armyworms.
  • Potato leafhoppers – Wedge-shaped insects up to 3 mm long; green bodies with yellow to dark green spots. They usually jump rather than fly. They suck sap from the underside of leaves causing yellowing of leaf tips and margins.
  • Fruit or vinegar flies – Small yellowish red-eyed flies about 3 mm long. They hover around overripe or decaying produce. They may be found with their small creamy maggots in cracks in sweet potatoes.
  • Tortoise beetle adults and larvae – Long-oval shaped gold beetles, up to 8 mm long, with various black or red markings on their flattened, shell-like bodies. The larvae have dull yellow, brown, or green bodies up to 12 mm long and black heads, legs, spots, and spines. Long spines on the abdomen hold excrement. Adults and larvae chew the leaves riddling them with holes.
  • Spider mites – Tiny reddish or pale spider-like arthropods that feed on the underside of leaves. Heavily infested plants develop a yellowish, bronzed or burned appearance.
Pests that feed underground on tubers and side roots
  • Sweet potato flea beetle larvae – Thin white, cylindrical larvae, up to 5 mm long, with 3 pairs of legs near their heads. They make shallow, winding tunnels on the surface of sweet potato roots and sweet potatoes. The tunnels darken, split, and leave scars.
  • Sweet potato weevil adults and larvae –Snouted beetles 6 mm long with dark-blue wing cases, orange-red legs and thorax, and fat, legless, 9 mm grubby white larvae with pale brown heads. The beetles make small holes over the surface of sweet potatoes mostly at the stem end. The larvae tunnel inside the tubers, leaving frass, which causes the sweet potatoes to taste bitter.
  • White grubs (spring rose beetles) – Dirty white grubs up to 25 mm long with brown heads and 3 pairs of legs near their heads. They leave large, shallow feeding scars on the sweet potatoes.
  • Wireworms – Thin, tough, wire-like larvae with 3 pairs of short legs near their heads and prolegs at the end of the body. They initially create large shallow cavities in sweet potatoes which they later excavate into deep ragged holes. Three species, with colors from yellowish-brown to cream or yellow-grey. Heads are darker, brownish.
  • White-fringed beetle larvae – Yellow-white legless, 12-segmented grubs, up to 13 mm in length, with small, pale heads. They chew into the roots.
Sweet potato souring.
Photo North Carolina Sweet Potato Commission
Afflictions of sweet potatoes (these are not caused by disease organisms) 
  • Round chunky roots, low yield, purple color: Planted too early, too cold.
  • Low yield: Flooded or crusted soil 6-7 weeks after planting? Planted too early?
  • Rough irregular shaped roots: Heavy clay soils or organic matter above 2%.
  • Rattails – thin, tough, tubers: Hot dry weather, insufficient water.
  • Long, slender malformed roots, reduced yield: Potassium deficiency.
  • Souring – Tissue breakdown caused by poor soil aeration, such as flooding.
  • Water blisters – Small whitish bumps around the lenticels (breathing holes): wet soil.
  • Blister – Small raised bumps appearing several months into storage: boron deficiency.
  • Fine hairline cracks: Another sign of boron deficiency.
  • Cracking: Uneven water supply or too much late-season water.
Sweet potato Ring Rot.
Photo North Carolina Sweet Potato Commission
Sweet potato feathery mottle virus.
Photo North Carolina Sweet Potato Commission
Diseases of sweet potatoes (mostly fungal)

 More info and photos: North Carolina State University Diseases of Sweetpotatoes. 

  • Brownish skin patches, worse in wet years: Scurf fungus, Monilochaetes infuscans. More likely if too much compost was used. Stored roots shrivel.
  • Metallic black surface lesions, maybe covering most of the root: black rot fungus, Certocystis fimbriata. Internal decay is not deep, but the fungus may impart a bitter flavor.
  • Sunken brown lesions that may completely encircle the root: ring rot, Pythium
  • Sunken lesions that dry and may fall out: Circular Spot, Sclerotium rolfsii. May taste bitter.
  • Hard, dry, black, sunken spots developing in harvest wounds: Fusarium. Spots may become larger than 2″ (5 cm) diameter, but damage is not deep.
  • Pitting: Soil rot or soil pox fungus in the presence of water stress. Roots will be small and malformed.
  • Streptomyces root rot bacterium causes a similar rot.
  • Fine or coarse irregular cracks, browning of the surface; dry, corky, dark-colored clumps of tissue scattered throughout the flesh, becoming worse if roots are stored warmer than 60°F (16°C): russet-crack/internal cork, feathery mottle virus (yellow feathery patterns of leaves). Do not use as seed stock.
When to harvest sweet potatoes

Unlike white potatoes, which have the annual plant sequence of vegetative growth, flowering and dying back, sweet potato plants would go on growing forever if the weather remained warm enough. Choose when to dig them up, ahead of cold weather. The longer you wait, the bigger the potatoes, but you are gambling with the weather. Usually sweet potatoes are harvested in the week that the first frost typically occurs in your region. I have written plenty already in previous years about harvesting, so I won’t go into it here. See one of the links to those posts, or my slideshow, if you want to know what comes next, or your climate is considerably colder than mine in central Virginia.

Our sweet potatoes next to our sixth sweet corn planting.
Photo Ezra Freeman

Potato pests and diseases

Potato pests and diseases

These potatoes were almost killed by frost two weeks previously, and have now recovered.
Photo Pam Dawling

This is part of a monthly series on growing potatoes, a dietary staple.

PART ONE: Planting potatoes (April)

PART TWO: Growing potatoes (May)

PART THREE: Potato pests and diseases (this one, June)

PART FOUR: Harvesting potatoes (July)

PART FIVE: Storing potatoes (August)

PART SIX: Planning to grow potatoes again (September)

I have a whole chapter about potatoes in Sustainable Market Farming, where most of this information can be found.

See Root Crops in June for info on digging up new potatoes, if you can’t wait for them to mature!

See The Potato Association of America, Commercial Potato Production in North America 2010 for lots of interesting info, including planting in hot weather. (But hurry up, you need to have enough growing days left in the season to get them to maturity.)

Organic Integrated Pest Management involves tackling pest problems one step at a time with ecologically-based practices, starting with actions to reduce the chances of the pest ever getting a grip on your crops. I recommend the ATTRA online publication Organic Integrated Pest Management. Each of the 22 pages is a poster, complete with good photos and concise clear info. Because nightshades have a lot of fungal, bacterial and viral diseases, it pays to take action to minimize the chance of diseases attacking your plants.

June-planted potatoes in early September
Photo Kathryn Simmons

Integrated Pest Management in Organic Field Crops Webinar from eOrganic

https://www.youtube.com/watch?v=nQXC8SElTMk

Biological IPM disease and pest reduction strategies for potatoes

  1. Cultivate strong crops and provide healthy soil, sufficient space, nutrients and water, suitable temperature, and soil pH.
  • Choose varieties that resist the pests and diseases you most expect. Improve the soil tilth, drainage and aeration. Chisel plow or broadfork to break hardpan, or grow deep-rooting cover crops ahead of your potatoes. Maximize air circulation around the plants. Choose a bright, breezy location (avoid frost pockets as they also collect dew), orient the rows parallel to prevailing winds and give the plants plenty of space.
  • Add compost and cover crops to build fertile soil to support strong plant growth and help increase the diversity of soil microorganisms, building naturally disease-suppressing soil. Use foliar sprays of seaweed extract, microbial inoculants or compost tea to boost general disease resistance. Consult ATTRA for compost tea Brew one part of compost to 5 parts water by volume for 14 days before spraying.
  • Practice crop rotation to reduce the chances of pests and diseases carrying over from one crop to the next. For potatoes, it’s best to rotate away from nightshade crops for at least three years. We don’t manage this ideal of one year in four. In our ten-year rotation, three of our ten years are nightshades (one paste tomatoes and peppers, two plantings of potatoes).
  • Practice good sanitation. Clear old crops promptly, so they don’t act as a breeding ground for pests or diseases. Avoid smoking, especially near nightshades, and have smokers wash their hands with soap or milk before working with potatoes. Tobacco can spread tobacco mosaic virus (TMV) to nightshade plants. Avoid working potato plants while the leaves are wet. Remove and destroy diseased plants, especially for late blight. Clean tools in between use in one field and another. When the harvest is finished, till the tops into the soil to speed decomposition, or remove and compost or burn them if growing on a small scale.
  • Remove nightshade weeds (e.g., horsenettle, jimsonweed and black nightshade), which can be alternate hosts for pests and diseases.
Potatoes, weeds and standing water. Don’t let this happen to you! Provide good drainage, remove weeds especially nightshade weeds.
Photo Bridget Aleshire
  • Prevent soil splash-back onto leaves, to reduce outbreaks of soil-borne diseases. Use drip irrigation rather than overhead sprinklers.
July photo of a mulched June-planted potato.
Photo Wren Vile
  1. Cover or protect the plants physically from the pests
    • mulches to stop soil-dwelling pests (CPB) moving up into your crops
    • netting or rowcover to protect from airborne pests (leaf hoppers, blister beetles)
  2. Provide habitat for natural enemies and other beneficial insects. Farmscaping with sunflowers, peas, vetch, buckwheat or small grains, to encourage ladybugs and lacewings, can make insect control unnecessary in a good year. Ground beetles and bats can consume surface and air attackers before you even need to look.
  3. Monitor your crops regularly at least once a week and identify any pests you see.
  4. Introduce natural enemies of the pest (bacteria, fungi, insect predators or parasites). Try biofungicides for use against some diseases. F-Stop, T-22G Biological Plant Protectant Granules or other forms of Trichoderma can control Rhizoctonia, Fusarium and Sclerotonia. Soil-Gard (Gliocladium virens) can work against Rhizoctonia. Bacillus subtilis works against Rhizoctonia, and Sclerotonia. Mycostop (Streptomyces griseoviridis) can be used against Phytophthora, Alternaria, 35% hydrogen peroxide diluted to a 0.5–1% foliar spray solution may help control early blight. 1% solution = 3.7 oz in 124.3 oz water to make one gallon (1 ml:33 ml). There are commercial products such as Oxidate that are based on hydrogen peroxide, which is corrosive and challenging to handle.
  5. Hand pick (or trap) and kill the pests if the pest population is above the action threshold. Many fruit and root crop plants can take 30% defoliation before suffering any loss of yield. Where the crop is the foliage, this may be too much, but people don’t east potato foliage!
  6. Use biological controls (often derived from natural enemies) if the damage is still economically significant after trying the earlier steps in the process, including Spinosad or Bt.
Colorado potato beetle on an eggplant leaf.
Photo Pam Dawling

Potato Pests

Potatoes can be attacked by more than 150 insect pests. But don’t despair! In each region there are only a few species that could cause unacceptable losses of yield or quality. These losses can result either directly from the insects or indirectly by transmission of diseases.

Colorado potato beetle is the most common pest that potato growers get to deal with. The pink blob-like larvae of this beetle can eat enormous amounts of potato leaves while growing into bigger pink blobs. Left alone they can kill a planting. Acceptable amounts of defoliation without causing loss of yield are surprisingly high: 50%–75% of the top leaves on a young 6″–8″ (15–20 cm) plant, 25% on a 12″–16″ (30–40 cm) plant, a mere 10% at the critical full bloom stage (when the tubers are sizing up), and up to 25% once full grown. As with many pests, having a few of them is not important — it’s all about the numbers. Action to control CPB is only needed if the number of adults or larvae is higher than 1.5 per plant or egg masses exceed one per ten plants.

Crop rotation is effective, because Colorado potato beetles overwinter as an adult in the soil and when they emerge they have to walk around searching for a potato plant. CPB can have 1-3 generations a year. Even where two or three generations are usual, a significant portion of the summer generation adults go directly into the soil and become dormant. Eggs are laid in clusters of 20 or more. They look like ladybug eggs but are a stronger orange color – don’t kill the wrong ones! The beetle can go from egg to adults in as few as 21 days. There are four larval instars, with 75% of the total foliage destruction caused by the final and fattest instar.

Colorado Potato beetle late stage larva or pupa.
Photo Pam Dawling

Mulching with hay or straw can prevent CPB finding your potato plants – we never find them on our summer planting. Our unmulched spring planting is a different matter. I scout that field once a week, counting adults and larvae on a hundred randomly selected plants. As soon as I see more than 50 adults or 150 large larvae or 400 small larvae per 100 plants, I unpack the sprayer. I do a spraying with Spinosad, a fermentation product of a soil bacterium. It kills insects by over-stimulating their nervous systems. Spinosad kills a wide range of helpful and harmful insects too, so spray in the early morning or late evening when bees are not flying. Shake the bottle well, and mix following the instructions. Clean and triple rinse the sprayer. Do not flush in the creek or pond. Repeat in 6 days, but only if needed. Usually one spraying is enough, although I continue weekly checks. In the South, there can be three generations of CPB each year, so stay vigilant.

Prior to using Spinosad, we used Bt. The version of Bt for CPB nowadays is Bacillus thuringiensis var. tenebrionis. The kurstaki strain (such as Crymax) generally available in small quantities previously is genetically modified, so we stopped using it, not wishing to be part of any support for GMOs.  Neem and Beauvaria bassiana can also kill CPB larvae.

Flaming when the potatoes are less than 8” (20 cm) tall, is another effective control measure for CPB. Choose a warm sunny day when the pests are at the top of the plants. Flaming can kill 90% of the CPB adults and 30% of the egg masses, according to Colorado Potato Beetle: Organic Control Options – ATTRA

Young eggplant struggling against lots of aphids.
Photo Pam Dawling

Insects with piercing-sucking mouthparts damage potatoes by physical injury to the leaves, sucking out phloem, injecting their toxic saliva and possibly transmitting diseases. While potatoes can grow new leaves, there is still damage to plant health. Direct injury by sap-feeding insects can kill the plant. Soil-dwelling insects have only minor effects on yield, generally, but can reduce tuber quality and storage life.

Aphid-transmitted viruses cause greater losses than all other insect-related damage together. There are at least 9 aphid-transmitted potato viruses. Aphids can be reduced by farmscaping, planting flowers which attract ladybugs, lacewings and other aphid-eating insects.

Clover flowers attract beneficial insects. Red clover in June.
Photo Pam Dawling

Potato leafhoppers are a bad problem in central and eastern North America. They overwinter on the Gulf Coast. In spring, flying adults are transported north on upper level airstreams. Yield loss can occur before visual symptoms are obvious. Leafhoppers can cause leaves to shrivel and die. The initial effects are reversible if leafhoppers are controlled before leaf tissue is destroyed (“hopperburn”). By reducing the green leaf area, hopperburn affects photosynthesis and growth. The most vulnerable stage is when the tubers are bulking up. Leafhoppers can also transmit diseases. Trichogramma wasps parasitize leafhopper eggs. Garlic with insecticidal soap, sprayed early in the morning, especially on the undersides of the leaves, can control hoppers.

Potato psyllid occurs in the western U.S. Damage to the roots and tubers is caused by feeding nymphs, which can cause psyllid yellows. The first symptoms of psyllid yellows include stunting, loss of green color, leaflet distortion, reddish discoloring of new leaves, and the appearance of aerial tubers. Early action can stop and even reverse the damage. Adults cause little to no damage underground.

Wireworms (click beetle larvae) can tunnel through the tubers. Wireworms can live for 1-3 years, so crop rotation is important. Avoid planting potatoes the first year after turning under pasture or lawn. If you expect to have wireworms, plant small whole seed potatoes rather than cut pieces. Cut slices of potato can be used to trap wireworms (dig up the trap pieces each day and kill the wireworms.

Cutworms can eat the leaves from the bottom of the plant up (the opposite approach from CPB larvae). Once the plants are fully grown, up to 75% loss of lower leaves is unimportant. At earlier stages, if any cutworm damage is seen, dig around the stem, find and kill the cutworms.

Blister beetles can cause trouble later in the season, skeletonizing leaves and spreading a wilt. They contain cantharadin, which can cause blisters on the skin of unwary workers. Blister beetles can be trapped in crops of chard or beets next to the potatoes. The beetles are easier to see and catch in the trap crops than in potato foliage. If there aren’t too many it may be worth putting up with them, as their larvae are carnivorous and eat grasshopper eggs.

The potato tuber moth damages both foliage and tubers during growth, but the biggest losses occur in storage. Larvae inside the potatoes can continue their development in storage, filling the tubers with frass and letting in decay organisms. When commercial infestations are high, the crop is not worth harvesting because of labor costs to cull out the infested tubers.

 Nematodes can be deterred by choosing appropriate preceding cover crops, or by applying 1-2 tons/ac (2240-4480 kg/ha) of crushed mustard seed meal to the soil before planting. This will also reduce early weeds and act as a fertilizer. 

Potato Diseases

Before a plant can become diseased, three conditions must exist: a susceptible host, a disease organism, and a suitable environment for the pathogen. The choice of the disease control method should be based on an accurate identification of the pathogen and the disease.

Late blight on a potato leaf. http://blogs.cornell.edu/livegpath/gallery/potatoes/late-blight/

Late Blight (Phytophthora infestans) is by far the worst disease to afflict potatoes. This is the disease that contributed to the famine in Ireland (caused by the profiteering of the English land-owners, who sold the barley and left the tenant farmers to subsist almost entirely on potatoes). The disease is caused by a species of a fungus-like oomycete or water mold (previously considered a fungus, now reclassified as protozoa) that blows in on the wind. It is worse in warm wet weather with cool nights. Late blight starts as “water-soaked” spots on the leaves. These expand into gray-black “scorched” areas, sometimes with a dotted white mold growth, especially on the underside of the leaves. Cut stems reveal a dark circle of infected tissue. The disease spreads rapidly, turning plants black, as if badly frosted, and can kill an entire planting in ten days unless stopped by hot dry weather.

The best defense is to always remove volunteer nightshades from your fields and compost or bury all crop debris. The disease spreads via cull piles, nightshade plants and petunias — it needs live plant material to survive. If you find volunteer potato plants popping up in early spring, it is best to pull them up! Spores survive winter in warmer climates and then blow north and uphill. Preventive action may be taken with sprays every five days of (toxic) copper products, hydrogen peroxide, Bacillus pumilus or Bacillus subtilis products.

If Late Blight occurs late enough in the season, you can save your crop by mowing off the foliage, raking it off and disposing of it, and leaving the field untouched for two weeks before harvesting whatever potatoes have grown. This prevents the spores getting into the soil and infecting the tubers. Disposing of large amounts of blighted foliage is no easy task. When I had to deal with Late Blight, back in the 70’s, we made a fire and gradually added more tops as the previous ones burned. This was a very smoky fire, polluting, and no doubt contributing to global warming. Digging a big hole and burying it all is probably better.

Early Blight (Alternaria solani) is a common fungal disease, which mostly affects stressed or older plants. It starts as small brown spots on the lower leaves, which conglomerate into brown blotches that are restricted by the leaf veins, and so they can be angular in shape. The lesions have a bullseye appearance – concentric circles with a yellow halo around each one. During warm humid conditions, the fungus steadily defoliates the plants, reducing yields. The disease is seed-borne, soil-borne and airborne, surviving on plant debris and nightshade weeds. Early blight (Alternaria solani) can appear late in the season, not just early, despite the name. The manifestation of blight symptoms can be minimized by growing strong healthy plants, supplying sufficient water, and spraying with compost teas. The beneficial fungus Trichoderma harzianum can give good results.

Black Scurf or Stem Canker fungus (Rhizoctonia solani) is worst in cold wet soils. Early in the season it can cause sprout death. On older plants, red-brown stem lesions develop into cankers, and the infection can spread to the tubers, which then become cracked and misshapen, and may have dead tissue at the stem end. There may be firm black sclerotia (small dried reproductive bodies) on the tuber. In future, get disease-free seed potatoes and wait for the soil to warm a bit before planting.

White Mold (Sclerotinia sclerotiorum) on the vines. If you want to prevent this in future, you could dust the seed pieces with the commercially available fungal antagonists Trichoderma viride and Trichoderma virens.

For a chart with about 30 potato diseases, see The Potato Association of America, Commercial Potato Production in North America 2010

A lady bug on a potato leaf, perhaps producing larvae to help control aphids.
Photo Kathryn Simmons

Everything You Need to Know About Garlic; Money and More

 

Softneck garlic ready to harvest
Photo Pam Dawling

We started harvesting our hardneck garlic on May 26 this year. One of the earliest harvests we have on record.

I’ve written lots on garlic in this blog, it’s one of the most sought-out topics. To cut to the chase, here’s my Garlic Recap.

Many of these are posts in my Alliums for the Month Series:

Harvesting garlic scapes
Photo Wren Vile

For a second opinion, see Margaret Roach (who grows in Massachusetts) in A Way to Garden

Music garlic cut open showing gaps around stem – a sign of maturity.
Photo Southern Exposure Seed Exchange

Of the many other posts I’ve written on garlic, that are not mentioned already, starting with harvest and moving round the calendar, there are:

Harvest

Garlic Harvest step by Step

Harvesting Garlic

Garlic Harvest

Garlic harvest, Intercropping, Summer lettuce,

Garlic harvest finished, fall crop planning, tomato bug heads-up

Garlic hanging in netting to dry and cure.
Photo Marilyn Rayne Squier

Drying and Curing, Snipping, Sorting and Storing

Garlic drying and curing methods

Snipping, Sorting and Storing Garlic 

Planting garlic

Sustainable Farming Practices slideshow, garlic planting, annual crop review

Garlic Planting and Freeing Trapped Shoots

Winter radishes, planting garlic.

Garlic scallions in March
Photo Pam Dawling

Garlic scallions

Harbinger weeds of spring, and early garlic scallions

Garlic scapes

Garlic scapes! Three weeks to bulb harvest!

Too much rain! But garlic scapes to cheer us up.

Garlic scapes

Garlic scapes, upcoming events, hoophouse seed crops

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My DONATE button

I’ve added a donate button, for those who’d like to use it (via PayPal or credit card). We’re all staying home, not going to conferences or fairs. This is reducing my opportunities to collect speaker fees or sell books face to face.

More people are reading my blog (thank you!). There are thousands of new or returning gardeners across the country, aiming to get fresh air and exercise while usefully putting their time into providing food for their households. There are experienced professional growers trying hard to make their farming more efficient, and pivot to find ways to still earn a living and not lose the farm, due to loss of markets.

I put a lot of energy into providing useful info and practical details, and so if you are finding my posts helpful, and you can afford to, please consider clicking the pay-what-you-can button.

Together we’ll get through this difficult time and reach better days again.

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Birth of Assassin Bugs

Debbie Roos, an Agricultural Extension Agent at Chatham County Center, North Carolina Cooperative Extension and the founder of www.growingsmallfarms.org is a wonderful photographer,. She recently reposted this.

A couple of years ago I posted a series of photos on my Growing Small Farms website showing assassin bug nymphs emerging from their eggs. It was an amazing thing to witness and not something you see every day. Folks really enjoyed seeing the photos back then and since it’s spring and time for more to emerge I thought it would be fun to share the photos again now that so many people are spending so much time at home!

Adult wheel bug feeding on a Japanese beetle. Photo by Debbie Roos. Click here to visit NC Cooperative Extension’s Growing Small Farms website to view the photos.

Be on the lookout for these egg clusters on your property and you may even get lucky and witness the birth of an assassin!

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Quick-Growing Vegetable Crops

Steve Albert has an informative website, Harvest to Table, and this post on quick-growing vegetables includes some warm weather crops like bush green beans and sweet corn. It includes names of fast-maturing varieties.

I wrote Fast Growing Vegetables in March, focusing on early spring crops. If you are still racing to catch up, or in need of more crops that yield quickly, see Harvest to Table.

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How to Fight Hornworms

On the Mother Earth News blog, my post How to Fight Hornworms has been very popular, and has led me to make an article for the Mother Earth Gardener magazine

This magazine is “a quarterly publication committed to giving you in-depth expertise to bolster your organic garden each and every season. Roll up your sleeves and learn soil-boosting strategies, permaculture practices, and more! Formerly known as Heirloom Gardener.”

Tobacco hornworm on tomato leaf
Photo Pam Dawling


16 things I know about growing tomatoes

From Margaret Roach at A WAY TO GARDEN

Margaret writes about home-grown seedlings, finding flavor, choosing between hybrids and open-pollinated varieties, saving seed, good tomato-hygiene, monitoring for pests and diseases, pruning, staking or otherwise supporting the plants, and dealing with the weather.

Jubilee tomato in our hoophouse.
Photo Pam Dawling

 

Planting Sweet Potatoes

Fresh sweet potato slips for sale from Southern Exposure Seed Exchange.
Photo Pam Dawling

Are you thinking about crops to grow that will feed a crowd next winter? Sweet potatoes are an easy crop to grow, provided your climate gives enough warm days. They store very well at room temperature, for a long time. In mid-late May, we are still eating sweet potatoes we grew last year, and they are delicious! Well grown and cured, sweet potatoes reach their peak in flavor during January and February. One baked sweet potato of 114gm (4 oz) has 185% the RDA of vitamin A, 28% the RDA of Vitamin C, 100% of vitamin E, lots of anti-oxidants, and 160 calories, none from fat.

Order some slips online and get the ground ready. You can order from Southern Exposure Seed Exchange 11 varieties, all organic, in bundles of 6–100. For more varieties but smaller orders, go to Sand Hill Preservation Center, Iowa. Heirlooms, 225 Varieties, all Organic. Some limits on how many you can buy. Another supplier I recommend is the Steele Plant Co, 10 varieties (not Organic) of slips in small (12) and large (500) quantities, good prices, great service. Slips are young shoots with stem, leaves and, usually, some roots. Sweet potatoes are not grown from seed or from chunks of potato.

I have known people grow sweet potatoes in hoophouses if their climate isn’t warm enough outdoors. This can fit with winter use of the hoophouse for greens and roots. My book Sustainable Market Farming contains a whole chapter on growing this crop, including growing your own slips, but it’s too late to start that this year.

Sweet potatoes fit easily into the crop schedule. Planting out comes later than most spring crops. It’s late enough to precede them with a mature cover crop mix (including legumes to the flowering stage), providing all the nitrogen needed. Or add an organic fertilizer this year and plan ahead for next year. Sweet potatoes do not need lots of organic matter, or high fertility levels. Fitting sweet potatoes into a rotation is easy because it is unlikely that you are growing anything else in that family. As with other crops, a three-year gap (or more) before planting sweet potatoes in the same beds helps control disease.

Modern varieties of sweet potatoes grow to a good size in as little as 90 days, so they are not just for the South! The further north you are, the longer the daylight at midsummer and the more photosynthesizing the plants can do.

Sweet potatoes thrive in hot weather and are fairly drought-tolerant. After vining they need little care during the summer (apart from irrigation) until harvest. Their extensive vines smother most weeds, and they have few pest or disease issues. Most of the labor is the harvest in early October, in-between most other intensive harvests of summer and fall crops. I’ll never complain about a crop which has most of the work be the harvest!

Understanding sweet potatoes

 Sweet potatoes are tuberous roots (Ipomoea batatas), related to morning glory, in the genus Ipomoea. Sweet potatoes or sweetpotatoes are native to the tropical regions in central and south America. The root is long and tapered, with a smooth skin, and color ranging from orange, yellow, beige, white, red, pink, violet and purple. Sweet potato varieties with white or pale yellow flesh are less sweet and moist than those with orange, pink or red flesh. The young leaves and shoots are sometimes eaten as greens. Hot weather greens are hard to find!

Sweetpotatoes are not yams, even though they’re often called yams! True yams are a tropical species of tuber (genus Dioscorea). They come from Africa and the Caribbean. Some are huge! They have rough and scaly skin. The flavor is starchy, and usually not very sweet (more like regular potatoes). Sweet potatoes will not even cross with yams.

Sweet potatoes are sometimes mistakenly thought to be a type of potato but they do not belong to the nightshade family, Solanaceae. Sweet potatoes are only distant cousins of the nightshade “Irish” (more accurately Peruvian) potatoes (Solanum tuberosum). Unlike Peruvian potatoes, which have the annual sequence of vegetative growth, flowering and dying back, sweet potato plants continue growing as long as the weather is warm enough. They are frost-tender herbaceous perennials.

A well-established young Georgia Jet sweet potato plant.
Photo Bridget Aleshire

Read more

 I have a Sweet Potato slideshow.

And I have written a lot of other posts on sweet potatoes (mostly about propagating our own slips, or about harvesting). Very little on actually growing them all summer. My posts include:

Starting Sweet Potato Slips

Sweet Potato Propagation and Yields

Transplanting Sweet Potatoes (biodegradable plastic; deterring deer)

Harvesting Sweet Potatoes (2016); Sweet Potato Harvest (2015) and again (2015) and earlier (2014) and in 2013, 2012

What Makes Sweet Potatoes Sprout (during storage)

I also have a blog post for Mother Earth News Organic Gardening blog, about growing sweet potatoes. And I have several articles in Growing for Market, which you can access online if you have a Full Subscription.

The vines of sweet potatoes start running after the roots have made good growth
Photo Bridget Aleshire

When to plant sweet potatoes

Figure out your ideal planting date. Planting is usually done about 2 weeks after the last frost. You need settled warm weather. Heat is vital. The soil temperature should reach at least 65˚F (18˚C) at 4” (10 cm) deep on 4 consecutive days—don’t rush into planting early. Plants set out too early will struggle with skin fungi, and produce uneven yields. Their growth will be stunted. Forget about climate zones—those are about winter-hardiness of perennials. Sweet potato growing is all about warmth and light. Your sweet potato plants can remain ignorant about your winter cold!

We plant May 10–20, between pepper, okra and watermelon transplanting dates. It takes 7–8 weeks to grow your own slips using our method, so buy slips for this year and learn how to save seed stock when you harvest, to grow your own slips next year.

Planning aheadhow many to plant

Decide how much space you want to plant, or how many pounds (tons?) you want to grow. One slip will produce a cluster of 4–10 roots, each weighing 3–17 oz (80–500 g). The yield range is 2.5–6.8 lbs (1–3kg) per plant, 276–805 lbs/1,000 ft² (14–40 kg/10 m²), or 6–17.5 tons/ac

The in-row planting space is 6–18” (wide spacing gives more jumbo roots). We do 15″ (38 cm) as we like to get some jumbos. If unsure, try 12” (30 cm). Climate, spacing, and the length of the growing season all affect yields.

The space between the rows could be 32–48” (0.8–1.2m). Calculate how many slips you’ll need and add 5–10%. For an acre you’ll need around 15,000.

Newly planted sweet potato slips with a motion sensor sprinkler to keep deer away. the wilting of newly-planted slips is common. Don’t despair!
Photo Pam Dawling

Sweetpotato crop requirements

 Sweet potatoes prefer loose, well-drained soil with pH of 5.8–6.2. They will tolerate pH from 4.5–7.5. Enough potassium (K) is important for drought-resistance, but too much K makes them taste bitter. Sweet potatoes do not benefit from high nitrogen (N). They can get plenty from high-biomass cover crops, organic mulch, and soil life.

Once they are established, sweet potatoes are fairly drought-tolerant. Critical times to maintain sufficient moisture are after transplanting and for at least the first 20–40 days while the roots are developing.

Tips to increase sweet potato yields

Compacted, heavy, lumpy soils can result in misshapen, undersized tubers. If you have clay soil or drainage problems, work in lots of compost and make raised beds or ridges 8”–12” (20–30 cm) high. Ridges help heat up the soil and reduce flood damage.

Black plastic or silage tarps set out 3 weeks before planting warm the soil considerably and increase the growth rate. In colder climates, plant under low tunnels of clear plastic. Ventilate in hot weather.

If it’s too cold to plant out your slips when they arrive, keep them indoors, with water covering the roots (remove any newspaper or other packing material). If you are planting in hot dry weather, water the soil first, and keep the roots enclosed in damp or wet compost as you plant.

We like to do two plantings a week apart, using the older slips first, and then do a third session to replace any casualties.

 

Young sweet potato plants with drip tape and ripped plastic mulch.
Photo Pam Dawling

Planting out sweet potato slips

 Prepare your beds or ridges. Get ready with your irrigation system. If you are covering the beds with biodegradable plastic mulch lay it out just before you will plant. Set out stakes and ropes to mark where the rows will be planted, and gather a measuring stick, trowel and watering can.

To grow the biggest roots, plant the slip vertically, which steers the plants to develop roots only from one node. To grow average size roots but many of them, plant slips horizontally 2–3” (5–7 cm) deep, encouraging tubers to develop at several nodes. Ideally, have 3–5 leaf nodes underground and only the tips above the ground—this gives the plants a second chance if a late frost strikes. Many growers have success with slips with few or no roots, but we like a good root system.

If you are using drip irrigation, run it while you plant. If the emitter spacing matches your plant spacing, plant in the damp spots without measuring. Otherwise, use a measuring stick or a double hand-span to get the plants evenly spaced and not waste plants or land, by diverging from your planned spacing. If you have driptape under mulch, feel for where the tape is, and avoid stabbing it with your trowel.

Firm the soil around each plant, so that it is not left sitting in an air pocket, unable to reach water.

If not using drip irrigation, stop every few plants and water from a watering can. Err on the side of too much water on planting day. Keep newly transplanted slips well-watered.

If it turns cold or windy soon after you transplant, you could use rowcover to protect the plants.

This motion sensor sprinkler has been working well to keep deer out of the sweet potato patch.
Photo Wren Vile

Sweet potato development

I usually reckon on the first month after planting being focused on root growth, the next month on vines and the rest on roots. Regardless of how early in the season you plant them out, they will not make flowers earlier, or start making tubers sooner. Both flower and tuber initiation are triggered by day length. Each variety has its own internal clock. Most varieties take 90–110 days from planting out to reach a good size, if the weather is warm enough.

The first month or so after transplanting is the root development stage. Roots can go 8’ (2.4 m) deep in 40 days. Don’t be alarmed at the lack of above-ground action. Give 1” (2.5 cm) of water per week, and cultivate to remove weeds. The second month or so is the vine growth stage. The roots begin to store starch and sugar close to the stem base. Cultivate until the vines cover the ground, after which very little weeding will be needed.

During the last month of growth for that variety (3rd or 4th month), the potatoes develop. Make sure you dig them up before the soil temperature gets down to 55˚F (13˚C) –the week of the average first fall frost is about right.

There are some pest mammals and insects, afflictions and diseases to watch out for, but usually sweetpotatoes will grow relatively untroubled until harvest time. Do watch out for deer, rabbits, and other rodents, or anything that appears to be reducing the leaf cover substantially. I’ll write more about these issues in a few weeks.

For more info, see ATTRA Sweet Potato: Organic production

North Carolina State University, Pests of Sweetpotato
North Carolina State University Diseases of Sweetpotatoes.

Growing Potatoes

Potato plant emerging in spring.
Photo Kathryn Simmons

This is the second part of a monthly series on potatoes. Last month I talked about Planting potatoes. Now they are in the ground, we turn our attention to growing healthy plants and doing all we can to maximize the yield.

Frosted potato plants May 10., after two nights at 30F and 29F. I hope this didn’t happen to you! If you know a frost is coming, try to get the potatoes hilled, which protects more of the stem and leaves under the soil. This increases the likelihood the plants will be able to grow back.
Photo Pam Dawling

Potato development stages and crop requirements

  1. First the plant produces roots, stems and leaves. This vegetative state lasts 30–70 days. Bigger plants have more yield potential, so the goal for this stage is to produce robust large plants. Vegetative (leafy) growth of potatoes is favored by warm, 80°F (27°C) moist weather, but tuber growth is favored by cooler soil conditions of 60°F–70°F (15.5°C–21°C). This combination can be achieved either by planting in spring, when the soil temperature lags behind increasing air temperatures and is still cool enough for tuber formation, or by adding organic mulches to keep the soil cool if planting in early summer.
  2. Tuber formation (a two-week process) and branching of the stems comes next. All the tubers (potatoes!) that will grow on that plant are formed in those two weeks. The number of tubers produced per plant depends on hours of daylight, temperature and available water in that short period of tuber initiation. Watering stimulates the production of more tubers. 5 gal/yd2 (22.8 l/m2) is a good amount to supply when tuber formation begins. Short day length is optimal, with a night temperature of 54°F (12°C). If temperatures at night are 68°F (20°C), initiation will be reduced; and at 84°F (29°C), will be inhibited. High nitrogen also inhibits initiation. During this stage, leaf growth continues. Flowering can happen too, but it’s not essential, so don’t worry if you get few or no flowers. Hilling adds soil to the stems, encouraging stem growth and providing sites for tubers to form.
  3. Third, the tubers grow larger, but don’t increase in number. When the leaves start to turn pale, the plant has finished its leaf-growing stage and will be putting energy into sizing up the tubers under the ground. Adequate water and nutrients are important during this critical stage which lasts until the plant reaches maturity for that variety, up to 90 days. Try to ensure at least one inch (2.5 cm) of water per week, up until two weeks before harvest. Avoid very uneven watering, or overwatering, as hollow heart could result. The size of the tubers depends on various growing conditions. Two or three weeks after flowers appear (if they do), the baby potatoes will be 1–1.6″ (2.5–4 cm) across. The best temperature is around 65°F (18°C), and I’ve read that potato size decreases by 4% for every Fahrenheit degree (7% per Celsius degree) above the optimal. Spacing is another factor — we got large potatoes one summer because we had poor emergence and therefore wide spacing! The heat of the summer didn’t stop them.
Three flat-tined potato forks to the left, four round-tined digging forks to the right. Flat tines do less damage, usually.
Pam Dawling

Potatoes dug during this tuber-sizing-up period will be “new” potatoes, and not have the thick skins necessary for storage. If you dig your potatoes during this stage (or “snitch” some, leaving the rest of the plant growing), you will be happy short-term, but your final total yield will be less than if you grew all the tubers to full size. If you planned for this, and grew plenty, you will be happy now, and happy later!

  1. Finally, the tops naturally yellow and die. The skins of the tubers thicken, which makes them suitable for storage. No more growth is possible. Sometimes there are reasons to terminate potato growth early – see Early Harvest below for more about this.

Hilling potatoes

Start hilling (pulling soil up over the plants in a ridge) when the plants are 6” (15 cm) tall. Hill again two or three weeks later and two more weeks after that, if the plant canopy has not already closed over, making access impossible. Hilling also provides an opportunity for dealing with weeds, so if possible do this task in sunny breezy weather which won’t let the weeds re-root.

Rows of potatoes after hilling.
Photo Wren VIle

On a small scale, use a rake or standard hoe to pull soil up from the side of the row opposite to where you are standing. If you are sharing the job, one person can work each side of the row at the same time. If you are alone, turn round and work back when you get to the end of the row. Don’t be tempted to twist your arms around and move the soil up the side nearest you. You will damage your body by this distortion of your spine and shoulders!

At the next scale up, use a rototiller with a hilling attachment, or perhaps a wheel hoe with a hiller, if your soil and stamina allows. We have used a semi-manual planting method, making single furrows with our BCS walk-behind tiller, planting by hand in the furrows, then using the tiller again to cover the seed pieces and hill. Nowadays we use a tractor-mounted furrower that can make two furrows in each pass, and disks turned inwards in pairs to ridge the soil.

Alternatives to hilling potatoes

If you can’t hill, you can increase the effective depth of planting by covering the rows with thick straw or hay mulch. This is easiest to do immediately after planting, before the plants emerge. We don’t mulch our spring-planted potatoes because we want the soil to warm up some from its winter temperatures.

Potato plant emerging through hay mulch in early July.
Photo Pam Dawling

When we plant in June, we cover the seed pieces, then hill, then unroll round bales of spoiled hay immediately, like wall-to-wall carpeting. We choose this method to help keep the soil cooler through the summer. In warm conditions, deeper planting, hilling and thick organic mulches all help keep the plants cooler, as does irrigation.

Weed control for potatoes

Potatoes are sometimes said to be a “cleaning” crop, as if they did the weeding themselves. Not so! Any cleaning that takes place is a result of cultivation. As with many plants, the initial growth stage is the most critical for weed control. Hilling in sunny weather can deal with lots of weeds in a timely way, especially if the machine work is followed up by the crew passing through the field hoeing. Organic mulches also reduce weeds. Potatoes later in life produce a closed canopy that discourages more weeds from growing until the tops start to die. Mary Peet reports that potato yields were decreased 19% by a single red root pigweed per meter of row left in place for the entire season.

Flame weeding can be used for potato plants while they are small, as well (as for carrots and beets before emergence as we see here).
Photo Brittany Lewis

In wet weather it can be impossible to hill when you’d like to, and this is where flaming can save the day. Flaming is not an alternative to hilling, but it can be a way to buy time and deal with rampant weeds if the soil is too wet to hill. Potatoes may be flamed at 6″–12″ (15–30 cm) tall. Beyond that, flaming is not recommended. See ATTRA for more on flame weeding. Flaming when the potatoes are less than 8” (20 cm) tall is also an effective control measure for Colorado potato beetles (More on pests next month). Choose a warm sunny day when the pests are at the top of the plants. Flaming can kill 90% of the adults and 30% of the egg masses, according to ATTRA.

Early harvest of potatoes

Sometimes there are reasons to terminate potato growth early. If you need storable potatoes, cut, flame or mow the tops of the plants, and wait two weeks for the skins to thicken up. To test for storability, dig up two potatoes and rub them together, or rub them firmly with your thumb. If the skins rub off, wait a couple of days before trying again. If the skins are strong, go ahead and harvest. You might do this if you have a fast crop turnaround after spring-planted potatoes, such as we used to do when following our spring potatoes with our fall cabbage and broccoli. Another time I’ve brought potatoes to a rapid end was in England, when we got Late Blight. We cut and removed the diseased tops (so no spores went down into the soil), and were able to salvage the potatoes two or so weeks later. Back then, the recommendation was to burn the green tops. This would probably not be recommended these days. It made for a smoky fire we kept going for several days. Terrible air pollution!

For the earliest possible crop in a dry climate (but not the highest yield), plant “old” seed (ones with lots of hairy sprouts) in early spring, hold off on watering until the tubers are marble size, then give a single good watering at 5 gal/yd2 (22.8 l/m2).

While it’s tempting to dig up potatoes early, the yields will be higher if you wait till the tops die.
Photo Kathryn Simmons

Next month I will write about potato pests and diseases.

Root Crops in May

A tidy bed of young carrots in May. Photo Kathryn Simmons

Root Crops to Plant in Central Virginia in May

Potatoes: It’s OK to plant any time in May: See my post on planting potatoes

Sweet potatoes: We generally plant sweet potatoes around May 10, 16″ (40 cm) apart, with 4-4.5′ (1.2-1.4 m) between ridges, allowing 5’ (1.5 m) space at the edges of patch. We install drip irrigation on the ridges when using plastic mulch. It is ideal if the soil temperature is 65°F (18°C) for four consecutive days before planting.  Plant 2-3” (5-7 cm) deep, with at least 2 nodes in ground, and at least 2 leaves above ground.  If the slips are long, plant them diagonally or horizontally, rather than going into a deep vertical hole, where the soil will still be cold. See my post on sweet potato planting

Carrots: We direct sow our sixth bed of carrots in mid-May. We sow our first carrots in mid-February, and then sow every 2-3 weeks after that. Our soils are cold in February, but the seed comes to no harm in the ground, and it’s a job we can get done early. May is our last month for sowing carrots that we know will be sweet. If we need to, we also sow once a month in June and July, but the hot weather impairs the flavor. Our big storage carrot sowing in early August will taste good, because the weather cools as they grow.

Here in central Virginia, zone 7, on a sandy clay loam, we grow Danvers 126, a sturdy open pollinated variety suited to high production of bulk carrots. In the past I have grown Chantenay Red Core (65 days), a blocky variety with a blunt tip, 5″ (13 cm) long and 2″ (5 cm) at the shoulder. It resists splitting, and can deal with clay.

Any decent soil will grow some carrots, but the best ones grow in deep, loose, and fertile sandy loams with good moisture-holding capacity. Old books warn against using manure before carrots as it will make them fork. This refers to uncomposted manure, not to compost. Compost will increase yields, and even reduce the culls with some varieties. (Research by Daniel Brainard at Michigan State University.) Compost not only increases the organic matter in the soil, but also suppresses some diseases and nematodes (which can cause forked carrots).

Thin carrots promptly to get good yields.
Photo Bridget Aleshire

Sow carrots whenever the soil is below 95°F (35°C), so long as you can keep the surface damp. Aim to sow 30 seeds/ft (1/cm), 0.25-0.5″ (0.6-1.2 cm) deep. Some people sow in single rows 8-10” (20-25cm) apart. Others sow in bands 2″ (5 cm) wide, at 8” (20cm) apart, with one length of drip-tape serving two bands in one 16-24″ (40-60 cm) bed. Carrots do well on raised beds, because the soil stays loose and the roots can easily grow deep. Hard rain in the first 3 or 4 days after planting can dry to a crust which could stymie the emergence. To prevent this, if you get heavy rain, irrigate for half an hour each day afterwards until the carrots emerge. Some people use shade cloth to help keep the soil surface moist. There are precision seeders which save you from thinning, but most growers I know use an EarthWay seeder, and then thin. Some people mix inert materials with the seed to help get a spaced stand. Sand at 1 quart (1 liter) to 0.5 teaspoon (2.5 ml) seed per 25’ (8 m) of row, is one recipe, although I worry that sand will destroy the plastic parts of the Earthway seeder before long.  Some people bake old carrot seed to dilute the good new seed.

Carrots do very poorly with competition, so try to start early carrots in a bed that had only light weeds the year before. Later sowings can make use of the Stale Seedbed Technique, where the bed is prepared ahead of time, and one or more flushes of weeds are germinated and flamed or hoed off. We flame weed our carrot beds before the carrots emerge. See the Special Topic below.

Carrots thinned to 1″
Photo Kathryn Simmons

Get to the initial thinning as soon as you can, spacing to about 1” (2.5 cm) apart, weeding at the same time. We usually have someone with good eyesight and hand-eye co-ordination hoe between the rows the day before the hand-weeding. If you are in an area with Carrot Rust Fly (Carrot Root Fly), you will want to remove all thinnings and broken foliage from the field, so you don’t lure the low-flying pest with the wonderful smell of the broken leaves. We do a second thinning, to 3” (8cm) at the stage when the baby carrots can be used for salads. If we get more weeds, we might do another round of weeding before harvesting the full size carrots. If carrots are spaced too widely, they will be more likely to split, and the overall yield will be reduced.

Flats of celeriac seedlings.
Photo Kathryn Simmons

Celeriac: An eye-catching winter storage root vegetable. Celeriac is sometimes called “turnip-rooted celery”. Its flavor is starchier and sweeter than celery, with hints of parsley, and a nutty taste. Celeriac is slow growing, but easy to care for once established.

If you have a long growing season, you could direct sow celeriac 6-7 months before the first fall frost date, for a late fall harvest. Perhaps put a board over the seed row to keep the soil damp and cool until the seedlings emerge. For most of us, we don’t have that much time. So if you didn’t already start some celeriac plants, May is too late for this year. Plan to order seed next winter.

Transplant celeriac when plants are 2.5-3″/6-7.5 cm tall, once the weather seems settled and warm, after your last frost date. If the weather is cold, just wait. Falling apple blossom is a phenology sign that conditions are suitable. We transplant celeriac around May 7 (our last frost is expected April 28). Use rowcover if a cold spell arrives after you have planted them out, or if you know cold weather is likely to return.

Celeriac gets 12”/30 cm spacing, with 4 rows to a 4’/120 cm bed –  that’s about 10”/25 cm between rows. We found closer spacing doesn’t work in our humid climate, as poor air-flow encourages rot. The Virginia climate is actually on the warm side for this crop, it prefers cooler areas, but we have good success if we pay attention at a few critical times. Celeriac requires long steady growth, so the task of the grower is to prevent checks to growth (such as weeds!). It can tolerate frost quite well, so there is no hurry to harvest in the fall. It can benefit from side-dressing with compost during the growing season, or giving seaweed as a foliar spray. A pH of 5.8-6.7 is ideal.

Root Parsley: A less well-known member of the umbelliferae family, also known as Parsley root, Hamburg parsley, Dutch parsley and turnip-rooted parsley. The flavor is a cross between carrot, celery and parsnip.  Like celeriac, it is slow to germinate and slow to grow. 70-90 days to maturity from direct sown seed.

Root Crops to Harvest in Central Virginia in May

Young beet plants
Photo Wren Vile

Beets: We like the long Cylindra/Formanova/Forono ones which are 6’’ (15 cm) long, very tender and are easily cut into regular slices, for pickles or cooking (55 days to maturity, OP). Among round ones we like Ace (50 days to maturity, F1 hybrid), and Detroit Dark Red (60 days, OP). Detroit Crimson Globe is said to maintain better flavor in hot weather than most others, which can develop off-flavors.

Young bunched beets can be stored for 10 days at 32°F (0°C) and 95% humidity. Mature beets can be stored for 6 months or more at 32°F (0°C) and 95% humidity. Trimmed beets keep well in perforated plastic bags under refrigeration.

Carrots: Our first carrots (sown in mid-February) will be ready to harvest in early May. Harvesting carrots barely needs describing. You need to loosen the soil to the depth of the carrots, pull them out, trim and wash. Some growers remove the tops first, but then it can be harder to remove the roots from the ground. Some people store them without washing, but then cleaning them is harder than if done before the soil dries on them. Carrots store very well in a refrigerator, in a perforated plastic bag. If you have lots to store, it is best to sort them, ensuring no scrawny ones or damaged ones get stored. Don’t store with apples or other fruit, or large amounts of cut flowers, or sprouting crops. The ethylene these crops give off can spoil the taste of carrots, removing the sweetness and leaving them tasting a bit soapy.

Harvested kohlrabi.
Photo McCune Porter

Kohlrabi: An unusual vegetable, sure to attract attention and be a discussion piece. It is tender with a flavor between a cabbage and a turnip. This tasty, crunchy root-like vegetable is easy to grow and doesn’t wilt as soon as you harvest it. It is actually the swollen stem, rather than a genuine root, but it behaves like a root vegetable. It can be eaten raw (sliced or grated) or cooked. The kind most commonly grown is a pale green or purple globe with long-stemmed leaves. When the leaves are cut off leaving stubs it resembles a sputnik. In addition, the leaves are also edible.

Conditions for growing kohlrabi are much the same as for other brassicas. It does best in cool weather. In our zone 7 climate, kohlrabi, like other brassicas, can be grown in spring or fall.

Harvest when the kohlrabi are 2-3” (5-7.5 cm) in diameter or even up to softball size. If left growing for too long the swollen stem becomes woody. Cut them from the ground with a sturdy knife. The base of the globe can be quite fibrous, so cut either the wiry root just below the soil surface, or cut higher, leaving a small disc of the globe behind, attached to the root. Snip or lop off the leaves, perhaps leaving a small top-knot if the kohlrabi will be sold immediately. We harvest in spring from around May 10 to June 30, and in the fall from October 20 to November 15.

Kohlrabi stores well in perforated plastic bags in a walk-in cooler, offering flexibility about when it is used, which is always an advantage.

Radishes: Early May brings an end to our spring radishes. Our last sowing is April 10. After then it is too hot for radishes where we are. In July or early August we sow winter storage radishes, including daikon.

Turnips ready for harvest.
Photo Wren Vile

Turnips:  A reliable root vegetable in the brassica family. They are among the fastest growing crops other than leafy greens. In zone 7, we sow a small crop of turnips outdoors under rowcover March 15, or earlier if spring is mild. Although they grow best in cool weather, turnips have no trouble germinating at high temperatures, as when grown for a winter storage crop.

Turnips are also available in gourmet varieties, to be eaten small, young and tender, 35-50 days after sowing, up to 2” (5 cm) in diameter. The delicious F1 hybrid Hakurei, 38 days, a smooth white flat-round shape, with crisp sweet flesh, and hairless leaves, is the most famous of the gourmet varieties. Although best harvested small, they do retain quality for a short storage period.

Young turnips can be pulled, banded, washed and sold with tops intact. Prompt cooling is important to keep the leaves from wilting. Small spring turnips can be pulled by hand, without digging – ours are ready May 20, and we clear the last of them in early June, refrigerating them till mid-July if we have enough.

For manual harvest, loosen the roots with a digging fork as needed, then pull. Trim tops and tails in the field (or move to the shade if it’s hot). All foliage should be removed for successful long term storage. Cut cleanly between the leaves and the root. Then wash, drain and store. Prompt washing before the soil dries on the roots will make them easier to clean.

Storage in perforated plastic bags under refrigeration works well for us. Turnips will keep for about 4 months at temperatures close to freezing and humidity of 90-95%. Higher humidity will make them rot.

Cut and damaged roots do not store well. If you haven’t enough humans to feed them to, but you have milking animals, you could chop them (to prevent choking) and feed them to your livestock. Even moderate quantities will not flavor the milk.

Other Root Crops Tasks in Central Virginia in May

See my post next week on growing and hilling potatoes, including alternatives to hilling for wet conditions. Flamers are intended to kill small weeds, not big ones, but we successfully used our wand-type flamer to kill weeds in the potato patch one spring when it was too wet to hill the potatoes.

Special Root Crop Topic for May in Central Virginia: Flame-weeding

When we sow carrots, we sow about 12″ (30 cm) of beet seeds at one end of the bed – these are “Indicator Beets”. When the beets germinate, we know the carrots will be up the next day and today is the time to flame weed the carrot beds. Flame-weeding is a great way to get rid of millions of fast-growing weeds and leave the field free for the slow-growing carrots. We still have to weed and thin once or twice as the carrots (and weeds) grow, but it is much easier to see the carrots, and they grow better if the first flush of weeds has been flamed off.

Soil thermometer in a beet bed.
Photo Bridget Aleshire

As well as beets, I use a soil thermometer and a chart of days to germination of carrots and beets at various soil temperatures. The table shows that beets are always a bit quicker than carrots in germinating. This information is in Sustainable Market Farming, Knott’s Vegetable Growers’ Handbook and Nancy Bubel’s New Seed Starter’s Handbook.

Days to Germinate 50°F (10°C) 59°F (15°C) 68°F (20°C) 77°F (25°C) 86°F (30°C) 95°F (35°C)
Carrots 17.3 10.1 6.9 6.2 6.0 8.6
Beets 16.7 9.7 6.2 5.0 4.5 4.6

Figure out which day you will probably need to flame. As soon as you see the red loops of the indicator   beet seedlings breaking the surface, flame the carrots. (But look for carrots too, just in case). In summer we flame carrots on day 4 after sowing, because we have found that carrots can emerge on day 5 in summer temperatures. One snag we hit once was that the carrots were mistakenly sowed an inch deep, instead of near the surface. Of course, this delays emergence, so by the time the carrots made it through that inch of soil, many new weeds had sprung up too.

Once you get over the hesitation about using a fiercely hot propane burner, flame weeding is quick and easy. And boy, it saves so much hand weeding! We use a Red Dragon backpack flame weeder (without the backpack frame).  We use the hand-held flamer attached to a propane cylinder that is in a wheelbarrow pushed by a second person behind the first. This person also acts as a safety monitor, looking out for unwanted things (like hay mulch burning). Some growers mount the propane on a backpack frame, and work solo, but we prefer to include a second person (and in this picture, a third!).

Flame weeding a carrot bed.
Photo Kati Falger

The operator walks along the aisle between beds, and wafts the wand diagonally back and forth across the bed. It takes about 10 minutes for a 100’ (30 m) bed. Flame weeding can reduce hand-weeding to one hour/100’ (30 m). Flame weeding plus stale beds 3 or 4 times can reduce hand weeding to 6 minutes/100’ (30 m).

Planting potatoes

Planting potatoes.
Photo Wren Vile

Planting potatoes

This is the first of a monthly series on growing potatoes, a dietary staple. Later parts will be

  • Part Two: Growing potatoes (May)
  • Part Three: Colorado potato beetle (and maybe other pests) (June)
  • Part Four: Harvesting potatoes (July)
  • Part Five: Storing potatoes (August)
  • Part Six: Planning to grow potatoes again (September)

I have a whole chapter about potatoes in Sustainable Market Farming, where most of this information can be found.

Potatoes are good food

Potatoes are a rewarding crop to grow, with a lot more flexibility about planting dates than the traditional instruction to plant on St Patrick’s Day might have you believe. As Carol Deppe points out in The Resilient Gardener (which I wrote about here), potatoes provide more carbohydrates per area than any other temperate crop, and more protein per area than all other crops except legumes. Many people are surprised to learn this. A 2,000-calorie all-potato diet contains considerably more protein than a 2,000-calorie all-rice diet. Potatoes contain 10.4 grams of protein per 100 grams dry weight, and are a good source of vitamin C and carbohydrates. Carol Deppe, has written a very interesting article The 20 Potato a Day Diet versus the Nearly All Potato Winter about the nutritional and gastronomic wonders of potatoes.  It will inspire you to grow and eat more potatoes!

The short version

Obtain your seed potatoes and set them to pre-sprout for 2-4 weeks. Then figure out where they’re going to grow and prepare the soil. Then plant and, before they emerge, figure out what to do next.

Potatoes emerging in spring.
Photo Kathryn Simmons

Potato planting dates and temperatures

Potatoes are a cool-weather crop, but the tops are not frost tolerant. A good guideline for suitable spring planting conditions is three consecutive days with a temperature at a depth of four inches (10 cm) exceeding 43°F (6°C). Some growers wait for soil temperatures to reach 50°F (10°C) before planting. A traditional phenology sign is that the daffodils should be blooming. The spring planting is usually timed with the goal of having most of the shoots emerge after the frosts. A light frost will only nip the tops of the leaves and do no real damage (the plants will regrow), so a small risk is worth taking. It takes a temperature of 29°F (–2°C) to kill the shoots, and even then regrowth is possible.

The practice of hilling soil over most of the leaves once the plants are six inches (15 cm) tall will protect against frost. So if you have plants growing and a frost is predicted, a hilling that day may save them. In the fall, frosts will kill the foliage and growth will stop, so late plantings should be timed to get the tubers to maturity before the expected frost date. Some late varieties do not bulk up until the last moment, so if you are pushing the late end of your planting season, plant early varieties or fingerlings. (“Early” = fast-maturing)

Here in central Virginia, we plant our first crop in mid-March, about four weeks before our last spring frost, and plant a second crop in mid-late June, which allows three and a half to four months before our average first frost date. We could plant any time mid-March to mid-June and harvest mature potatoes. In summer, the ideal soil temperature is 60-75°F (15-24°C). It’s possible to pre-irrigate to lower the soil temperature in summer.  If we wanted to, we could plant a fast-maturing variety in July.

If you want to plant at “unusual” times of year, you may need to plan ahead, buy your seed when it’s available and store it in a cool dark place below 50°F (10°C), such as a refrigerator, until you need it. Many suppliers only ship in March and April. Growers in zones 8–10 may need to buy their spring seed potatoes in the previous fall. We buy our seed potatoes for the June planting in April, before local suppliers sell out of spring stocks. An advantage of summer planting is that the harvested crop need only be stored from October or November, not over the hotter months.

A grower specializing in many kinds of fingerlings might want to plant once a month during their season, for a continuous supply of fresh new potatoes. Growing in a hoophouse offers another option for growing for a late market, for example new potatoes for winter holiday dinners.

Planting seed potatoes by hand.
Photo Ira Wallace

Dormancy

Potatoes have a dormant period of four to eight weeks after harvest before they will sprout, so if you plan to dig up an early crop and immediately replant some of the potatoes for a later crop, it won’t work. Get around this problem by refrigerating them for sixteen days, then pre-sprouting them in the light for two weeks. Apples, bananas or onions will help them sprout by emitting ethylene.

Potato planting quantities

If using 10″ (25 cm) spacing, we buy enough to plant 16–17 lbs/100′ of row (around 1.2 kg/10 m). 12″ (30 cm) spacing is more common, providing bigger potatoes than at 10″ (25 cm), although yields may be lower. For 12″ (30 cm) spacing, the recommendation is to allow 10–12 lbs/100′ (7–9 kg/10 m). In practice, we need a higher seed rate, maybe 15 lbs/100′ (11 kg/10 m).

Varieties

The many varieties of potatoes are generally divided into four categories.

  • Early potatoes take 55–65 days from planting to harvest — the more famous ones include Yukon Gold, Irish Cobbler, Red Pontiac and Caribe.
  • Mid-season potatoes mature in 70–80 days, and include Kennebec, Katahdin, Desiree and Yellow Finn.
  • Late-maturing varieties take a full 85–120 days to mature and include Russet Burbank, Butte and Green Mountain.
  • The fourth category is fingerling potatoes, which are small, attractive and have a high market value. They are prolific and no harder to grow than other potatoes.

Farms that are not certified organic have the option of buying non-organic seed potatoes locally, which saves money on shipping. Be sure, though, to buy seed potatoes that are certified disease-free. Late blight is a disease not worth risking. Some growers buy “B” potatoes that are small enough to plant without cutting. For most growers, “B” potatoes are not available, and we settle for larger seed potatoes, which have fewer eyes for the weight than small ones do, and need to be cut into pieces before planting.

Pre-sprouting potatoes

Pre-sprouting, also called chitting or green-sprouting, is a technique to encourage seed potatoes to start growing sprouts before you put them in the ground. It’s not essential, but advantages are:

  • getting an earlier start on growth in the spring;
  • being less dependent on outdoor weather conditions;
  • giving the potatoes ideal growing conditions early on and so increasing final emergence rate;
  • bringing harvest forward 10–14 days;
  • increasing yields by optimizing the number of sprouts per plant;
  • making the cutting of seed potato pieces easier (the sprouts are more obvious than eyes);
  • enabling cover crops or food crops to grow longer before the land is needed for the potatoes;
  • giving you the chance to prepare and irrigate the soil as needed before planting.

To start the sprouting process, bring seed potatoes into a warm well-lit room, around 65°F–70°F (18°C–21°C), and set them upright in shallow crates or boxes, rose (eye) end up, stem (belly button) end down, for 2–4 weeks in spring, or 1–2 weeks in summer. If you have no space or time for chitting, warming the potatoes for a couple of weeks (maybe even just a couple of days) will be beneficial. Some people like to warm the potatoes in the dark for two weeks, then spread them out in the light for the last two weeks before planting. I don’t know if the two-part process offers advantages, because I’ve never tried it. In the light, the growing shoots will grow green and sturdy, not leggy and fragile. Make sure the potatoes have a moist atmosphere so they don’t shrivel while they are sprouting. At this point don’t worry if a few sprouts break off; more will grow later.

In spring, the sprouts will grow considerably faster with indoor warmth than they would if planted unsprouted in cold ground, where they could take as long as four weeks to appear. Once planted, chitted potatoes will emerge sooner, and more evenly, which is always reassuring, and the weed competition will not be as fierce. Fewer seed pieces will die before emerging. And if weather prevents soil preparation when you had planned, just wait and know that your plants are growing anyway.

For summer planting, encourage sprouting success by storing seed potatoes in a cool place like a refrigerator, at 45°F– 50°F (7°C–10°C) until two weeks before planting time, then sprouting and cutting them. This encourages the lower eyes as well as those at the rose end to sprout. For warm-weather planting, one sprout per seed piece is usually sufficient. Tubers with many sprouts can be cut into many seed pieces, which can save money.

Cutting seed potato pieces.
Photo Kati Falger

Cutting potato seed pieces

Before planting, cut the seed potatoes (unless already small) into chunks about the volume of a ping-pong ball and weighing 1–2 oz (30–60 g) each, with the smaller fingerlings at 0.7–1 oz (20–30 g). Within a reasonable range, the size of the seed piece has little effect on the final yield, so long as it doesn’t shrivel before growing, and has enough food reserves to get the stem up into the sunshine. Cutting large potatoes is more economical than planting them whole.

For cold-weather planting early in the year, aim for two sprouts per piece, which allows one for insurance if the first one gets frosted off after emergence. For warm-weather plantings, one sprout per piece is enough. Extra sprouts can be rubbed off when planting. Planting seed pieces with too many sprouts will cause only small potatoes to grow, as each stem is effectively a single plant and will be competing with the others for light and nutrients. Also, overcrowding can force tubers up through the soil, and they will turn green if they reach the surface.

Cutting does “age” the seed, leading to weaker sprouts, and the final plant size will be smaller and the plants will die sooner. The total yield will be lower (although earlier) than from “younger” seed. Young unsprouted seed potatoes can be cut and then held at about 50°F (10°C). We often keep ours at 65°F–70°F (18°C–21°C). Older seed should not be kept above 45°F (7°C). Since sprouting ages the tuber, temperatures should be lower for seed that has already sprouted.

We usually cut our seed 1-3 days before planting. Varieties like Atlantic and Kennebec have slow healing abilities, and are best cut ahead of time. Up to 14 days ahead of planting is OK for cutting pre-sprouted potatoes. Unsprouted potatoes can be cut as much as a month ahead, although my choice would be to sprout them for at least two weeks and then cut pieces. It is more challenging to cut unsprouted potatoes, because there’s no knowing which eyes will actually sprout. I think cutting immediately before planting only works in warm dry conditions, as the unhealed surfaces can rot in cool wet conditions. Delayed emergence and patchy stands are signs of planting the seed in soil that was too cold, too wet or even too dry. Erratic and slow plant growth interferes with timely hilling; smaller plant canopies offer less weed competition.

Cutting seed potato pieces.

Make clean cuts with a sharp knife, aiming for blocky pieces about 1–2 oz (30–60 g) each. Avoid cutting thin slices or slivers, as these may dry out and die rather than grow. The cuts should not be too close to the eyes. Reject any potatoes with no sprouts. Some people cut their potatoes a few days ahead of planting and put the pieces back into the crates to allow the cut surfaces to heal over. For large quantities you may need several layers deep. If so, use fans to keep a good air circulation. Relative humidity of 85 – 95% is needed to promote healing and avoid dehydration. Some people coat the cut surfaces with sulfur or bark dust to help suberization (toughening of the cell walls).

See the University of Maine Extension Service Bulletin #2412, Potato Facts: Selecting, Cutting and Handling Potato Seed for lots of details. These drawings come from their bulletin.

Seed potato pieces after pre-sprouting for planting.
Photo Kati Falger

Planting your potatoes

Potatoes need to have a good final depth of soil and/or organic mulch above the seed piece. All the new potatoes grow from the stem that grows up from the seed piece. None will grow below the seed piece, so be sure to plant deep enough and hill up and/or lay on thick organic mulch to provide plenty of space for your crop.

Row spacing of 32″–45″ (80–115 cm) is common, with in-row spacing of 10″–15″ (25–38 cm). In early spring, when the soil is cold — if you want fast emergence and can hill up two or three times — you could plant shallow: as little as one inch (2.5 cm) deep in the North and four inches (10 cm) deep in the South. This technique helps avoid Sclerotinia problems. When the chilliness of deeper soil is not an issue, plant deeper, especially if your chances to hill might be restricted (for instance, by too much rain).

Dig furrows (by machine or by hand) at the chosen depth, normally 4-6” (10-15 cm). Add compost if possible. Plant the potatoes, sprouts up. Take care not to bruise the seed pieces when planting. If you are planting by hand, have some kind of measure – your foot, a stick or the width of the crate. Cover with at least 2” (5 cm) of soil. Later more soil will be piled up against the stems, in the process called “hilling”.

Row of seed potato pieces aligned under a rope.
Photo Ira Wallace
Photo Ira Wallace

When plants are 8-10” (20-25 cm) tall, they need hilling. I’ll cover this more fully next month.

An alternative planting method for those with lots of organic mulch, is to set the potatoes on the surface of the (loose, not compacted) soil, and cover with 12” (30 cm) of loose straw or hay.

Potatoes can be grown in containers, such as drums, barrels, large bags. I don’t recommend stacked tires as these often contain too much toxic dust and particles.

Also see Harvest to Table How to Grow Potatoes

Spring potato rows, in need of hilling.
Photo Wren Vile

Cooking Greens in April

Cooking Greens to Harvest in Central Virginia in April

Out with the old! In with the new!

A bed of spring Senposai.
Photo by Wren Vile

Outdoors, collards, kale and spinach that have over-wintered will be coming to an end. Most years, the collards and then the kale bolt in mid-late March, and the overwintered spinach in April.

Fast growing crops like mustard greens and senposai from spring transplanting will be ready to harvest as leaves from early April; collards and kale from mid-April. Beet greens might be ready at the end of April, or it might be May before we get those, depending on the weather and our sowing dates.

From the hoophouse, we are getting the last of most of our indoor greens. The Russian kale, the chard and the Frills (frilly mustards) are bolting. We do have spinach we sowed in January, which will continue all this month. The Bulls Blood beet leaves no longer look very appetizing, but we could cook those up early in the month. The milder winter means earlier bolting this year.

Cooking Greens to Sow in Central Virginia in April

Bright Lights chard in our garden in July.
Photo Pam Dawling

Chard is our best summer cooking green. Chard (Beta vulgaris var. cicla) is the same species as beetroot and, like beets, is a biennial. Hence it will not flower until the second year after planting, and can provide fresh greens all summer and fall, until halted by hard frosts. Even then, the root may survive and regrow the next spring. Leaf beet, also known as perpetual spinach, is a chard, with thinner stems and smaller leaves than most Swiss chard. It is the closest in flavor to spinach for growing in hot weather

Leaf Beet (Perpetual Spinach)
Photo Fedco Seeds

If you prefer spinach in spring, as we do, grow that first, and switch to chard for summer, sowing in plug flats or soil blocks three weeks before your last frost date. (We sow March 24-April 6)

If you want chard in spring, you can start flats earlier or direct seed outdoors two or three weeks before the last frost date.

We also use beet greens for cooking, although our main purpose is to grow beets. Our last date for sowing beets in spring is 4/15.

There are other hot weather greens you could sow in central Virginia and warmer climates.

In the hoophouse, it is definitely too late to plant cooking greens. Anyway, we are filling the tunnel with early tomatoes, squash, cucumbers, and peppers.

Cooking Greens to Transplant in Central Virginia in April

Broccoli head after rain
Photo Wren Vile

Outdoors, we transplant our main cabbage and two sowings of broccoli under nets or rowcover within 6 weeks of sowing. Rowcover is our usual choice, because changeable weather and late frosts are more of an issue here in spring than bugs are. It is important to protect young cabbage and broccoli with 5-8 true leaves from cold stress (<40°F/4.5°C for a few days, or longer at 50°F/10°C). At this stage they are particularly sensitive to cold, which can cause early bolting (and very low yields). After a few weeks, when the weather is more settled, we move the rowcover to newer, more tender crops.

Mid-April: We use saved extra transplants to fill gaps in the broccoli and cabbage plot, at the same time planting out alyssum every 6’ (1.8 m) in the center of the beds. These little flowers attract beneficial insects (see more below).

Ruby Red chard.
Photo Kathryn Simmons

Late in April we will transplant leaf beet and chard – it doesn’t take long for the seedlings to grow. Often we cover the prepared bed with hay mulch, then make two rows of “nests” in the 4’ (1.2 m) wide beds. We don’t space the rows evenly across the bed, but bunch them in close to each other in the middle. This saves the paths for us to walk down.

In the hoophouse, in very early April we use young spinach transplants to fill gaps only in the outer thirds of the beds, leaving the bed centers free for the tomatoes, etc. It would be better to have done this in late February and March, but this year we didn’t get to it. We won’t get high yields, planting this late.

Other Cooking Greens Tasks in Central Virginia in April

Early April: We move rowcover from turnips, senposai, early cabbage, kohlrabi and onions as needed for the broccoli and the maincrop cabbage.

Mid-April: We move rowcover from spring-planted kale, collards, mustard and early lettuce for the tender crops. We finish filling gaps in the broccoli and cabbage plot, at the same time planting out alyssum (sown March 3) one plug every 6’ (1.8 m) in the center of the beds. See the Special Topic for April below, for more on farmscaping, as this method of pest management is called.

Early spring cabbage with alyssum to attract beneficial insects.
Photo Pam Dawling

Late April: We move rowcovers from for the broccoli and the maincrop cabbage. With broccoli, the first weeks after transplanting are vegetative growth, adding leaves until there are about 20, when “cupping” starts — the leaves start to curl up, forming a convex shape rather than growing straight out. The cupping stage is usually10-14 days before harvest starts, depending on temperature. If the weather gets too hot — more than 80°F (27°C) — too soon, the broccoli may grow only leaves, and not head up.

In the greenhouse, we start to have less work, which is fortunate as outdoor work increases.

Special Cooking Greens Topics for April: Farmscaping for Brassicas

Farmscaping is the inclusion of specific flowers to attract beneficial insects. The pollen and nectar offer an alternative food source to beneficial insects when their insect prey is scarce. And if their insect prey is right by the flowers, what could be better?

Alyssum.
Photo Raddysh Acorn

We plant Sweet Alyssum in our spring broccoli patch to attract predators of aphids and caterpillars; Putting 5 percent of the crop area in plants that attract beneficial insects can seriously reduce pest numbers. Sweet alyssum, yarrow, dill, coriander (cilantro), buckwheat, mung beans, other peas and beans, black oil-seed sunflower, calendula and cleome all work well to attract a range of insects (especially ladybugs and lacewings) that eat or parasitize aphids. Pans of water and gravel will help attract aphid midges and lacewings. The gravel provides surfaces for the insects to land on while drinking. Farmscaping can make other insect control unnecessary in a good year. Beneficials will generally move up to 250 feet (75 m) into adjacent crops.

We also plant “insectaries” around the garden, usually at the ends of beds with crops that will be growing for several months. These flowers are planted inside rings sawn from a plastic bucket. The rings alert the crew that something special is there, not just a clump of weeds. Mix flowers to have something blooming all the time.

Insectary circle with sunflower, tithonia, borage, zinnia.
Photo Pam Dawling

Another method for incorporating farmscaping is to plant beneficial-attracting perennial flowers in areas that are too challenging to use for production: edges, slopes, tight corners, hedgerows, and field borders.

Other Pest Management for Brassicas

Using rowcovers keeps many pests off the plants while they are small. We have not had much trouble with aphids, perhaps partly because our overhead sprinklers wash them off and they can’t travel far. Insecticidal soap sprayed three times, once every five days, can usually deal with aphids. Our worst pest is the harlequin bug. For lack of a better organic solution, we handpick them. Ladybugs are reputed to eat harlequin bug eggs.

Sometimes we have had enough cabbage worms to make Bt (Bacillus thuringiensis) necessary, but usually paper wasps eat the caterpillars. The action level threshold is an average of 1 cabbage looper, 1.5 imported cabbageworms, 3.3 armyworms or 5 diamondback moth larvae per 10 plants. Below this level you can do watchful waiting rather than spraying with Bt or spinosad. We are lucky enough to have the naturally occurring wasp parasite of cabbage worms, the Braconid wasp Cotesia species, which are found as small cottony white or yellowish oval cocoons in groups on brassica leaves. The Cotesia wasps like umbelliferous flowers, and overwinter on yarrow as well as brassicas. If you find Cotesia cocoons in the fall and your brassicas aren’t diseased, you can leave plants in the field over winter. Or you could collect up leaves with cocoons in late fall and store them at 32°F–34°F (0°C–1°C) until spring. Hopefully no one will clean out your fridge without checking.

Richard McDonald has good information in his Introduction to Organic Brassica Production. He reports that broccoli plants with six to sixteen leaves (just before cupping) can lose up to 50 percent of their leaf area without reducing yield. Moderate defoliation (20–30 percent) causes the plant to exude chemicals that attract parasitic wasps and predatory insects. If you relax and allow this amount of defoliation early on, you can encourage these beneficial insects to move in and begin foraging in the area. Once the plants cup, you want to prevent further defoliation by having the most beneficials and the fewest pests on site. If pest levels are above the action threshold, cupping is the stage to take action, and probably not earlier.

Broccoli side shoots offer harvest after the main head is cut.
Photo Nina Gentle

To float out worms and aphids after harvest (before cooking!), use warm water with a little vinegar and soak for up to fifteen minutes, then rinse.

Fast Growing Vegetables

Lettuce bed in May.
Photo Wren Vile

Maybe part of your response to Covid-19 is to grow more of your own food, and you are wondering what can bring fastest results. Or maybe you just want to leap into spring and have early harvests. Either way, here is information on some vegetable crops that offer fast returns; ways to get crops to grow faster; ways to get more crops from a small space and some sources for more information.

Vegetable Crops That Offer Fast Returns

In my blog post If Spring is Too Wet in March 2019, I included a paragraph on fast crops.

  • Ready in 30–35 days from sowing are baby kale, mustard greens, collards, radishes, spinach, chard, salad greens (lettuce, endives, chicories) arugula, and winter purslane. Beet greens from thinnings can be cooked and eaten like spinach.
  • Many Asian greens are ready in 40 days or less: Chinese Napa cabbage, Komatsuna, Maruba Santoh, mizuna, pak choy, Senposai, tatsoi, Tokyo Bekana and Yukina Savoy). See my Asian Greens of the Month category of posts. There’s a huge range of attractive varieties, they’re better able to germinate in hot weather than lettuce, and faster growing than lettuce. Most reach baby salad size in 21 days, full size in 40 days. Transplant 4-5 weeks after spring sowing, or direct sow. Nutritious as well as tasty. Flavors vary from mild to peppery; colors cover the spectrum: chartreuse, bright green, dark green and purple. A diversity of crops without a diversity of growing methods! Grow when you normally grow kale. Be aware that Asian greens sown in spring will bolt as soon as the weather heats up, so be ready to harvest a lot at once (if you planted a lot, that is!) You can make Kim Chee.
  • Tatsoi and our August sown catch crop of Tokyo bekana.
    Photo Pam Dawling
  • One summer we sowed Tokyo Bekana as a lettuce substitute. 20 days to baby size, 45 days to a (large) full size. We have also grown this at other times of year, when faced with an empty space we hadn’t planned for.
  • Mizuna and other frilly mustards are very easy to grow, and tolerate cold wet soil to 25°F (-4°C). In addition, they are fairly heat tolerant (well, warm tolerant). Use for baby salads after only 21 days or thin to 8″–12″ (20–30 cm) apart, to grow to maturity in 40 days. Mild flavored ferny leaves add loft in salad mixes and regrow vigorously after cutting.
  • Also ready in 30–35 days are spinach, chard, salad greens (lettuce, endives, chicories) and winter purslane.
  • Ready in 35–45 days are baby carrots (thinnings or the whole row), turnip greens (more thinnings!) endive, corn salad, land cress, sorrel, parsley and chervil. Some of the faster smaller turnip roots can also be ready in 45 days or less.
  • Ready in 60 days are beets, dwarf snap peas, broccoli, collards, kohlrabi, turnips and small fast cabbages (Farao or Early Jersey Wakefield).
  • Also ready in 50-60 days once we are past frosts: zucchini, yellow squash, bush beans, small cucumbers can grow fast.
  • Garlic scallions can be grown over-winter, but will grow quickly in spring. Plant scrappy little garlic cloves you don’t want to cook with in close furrows and wait till the leaves are 7” (18 cm) tall before digging up the plant and preparing like onion scallions (spring onions). Can be eaten raw, but more often cooked. You can also plant whole bulbs without separating the cloves. This is a good use for extra bulbs that are already sprouting in storage.
Our garlic scallions in February. we usually space the rows much closer than this. We’ll start harvesting when they reach 7″ in height.
Photo Pam Dawling
  • See other blog posts in my Cooking Greens for the Month series, and Asian Greens for the Month, as well as Lettuce of the Month
  • Try Eat-All Greens, an idea form Carol Deppe. Patches of carefully chosen cooking greens are sown in a small patch. When it reaches 12″ tall, Carol cuts the top 9″ (23 cm) off for cooking, leaving the tough-stemmed lower part, perhaps for a second cut, or to return to the soil.
Twin Oaks Eat-All Greens on October 19.
Photo Bridget Aleshire
  • Spinach is good for salad or cooking uses. Be aware that the fastest biggest spinach may not last long once it warms up! We have found Acadia and Reflect have good bolt-resistance from outdoor spring sowings.

Fast Varieties of Lettuce and Greens

Bronxe Arrow lettuce.
Photo by Southern Exposure Seed Exchange
  • Grow the right lettuce variety for the conditions. Ones that do well in early spring are often useless here after the end of March, or even mid-February. I like to sow 4 varieties each time (for the attractive harvests, and to reduce the risks if one variety bolts or suffers disease): at least one red and one romaine. We have 5 lettuce seasons, with different varieties:
    • Early Spring (Jan – Mar), 6 sowings
    • Spring (April – May 15), 5 sowings
    • Summer (May 15 – Aug 15), 17 sowings (lots of seed!)
    • Fall (Aug 15 – Sept 7), 9 sowings
    • Winter Sept 8 – 27, 9 sowings
  • Baby lettuce mix can be ready in as little as 21 days from mid-spring to mid-fall. A direct-sown cut-and-come-again crop, the plants regrow and can be harvested more than once in cool seasons. Weed and thin to 1″ (2.5 cm). When 3″–4″ (7.5–10 cm) tall, cut 1” (2.5 cm) above the soil. Gather a small handful in one hand and cut with using large scissors. Immediately after harvesting, weed the just-cut area so the next cut won’t include weeds
  • Leaf lettuce can be harvested by the leaf much sooner than waiting for a whole head of lettuce.
  • Small-leaf lettuces (aka Eazyleaf, One-Cut, Multi-Cut, Multileaf): Johnny’s Salanovas, Osborne’s and High Mowing’s Eazyleaf; Tango, Oscarde, and Panisse (older varieties) too. Full-size plants can be harvested as a head, or harvested with a single cut, providing a collection of bite-sized leaves. Or just one side (or the outer leaves) of the plant can be cut and the plant will regrow for future harvests. Growing multileaf heads takes 55 days, compared to 30 days for baby lettuce.
Buckley red oakleaf single-cut multi-leaf lettuce.
Photo High Mowing Seeds
  • Other greens can be sown in close rows for harvesting as salad crops at a height of 3”-4” (7-10 cm). These are called mustard mixes or brassica salad mixes.
  • Many cooking greens can be used as salad crops while plants are small, as you thin the rows of direct-sown crops.

Ways to Get Crops to Grow Faster

  • Sow when the conditions are right. Soil temperature is important. I have a table of soil temperatures in Year-Round Hoophouse on page 208. Vegetable Seed Germination: Optimum soil temperatures for germination and days to emergence, where known.
  • Grow transplants. By starting your plants in a place with close-to-ideal temperatures, rather than direct-seeding when it’s still a bit too chilly outside, you’ll get bigger plants sooner. You’ll also buy time to prepare the soil where you are going to plant out.
  • Find warm sheltered micro-climates, in front of a south-facing wall for example.
  • Make your own warm sheltered micro-climates with rowcover or low tunnels.
  • Take advantage of plastic mulch to warm the soil, for crops that like warmth. Regular black plastic mulch will need to be removed at the end of the growing season, but biodegradable mulch does not. However, if you are taking over part of your yard near your house, I should tell you that you will see shreds of the bioplastic next year. See Setting out biodegradable plastic mulch by hand
Rolling biodegradable plastic mulch by hand
Photo Wren Vile
  • Consider landscape fabric with planting holes burned in, as a reusable alternative to throw-away or biodegradable mulch.
  • Use mixes for salads: Our general salad mix harvesting approach is to mix colors, textures and crop families. I like to balance lettuce of different kinds with chenopods (spinach, baby chard, Bull’s Blood beet leaves) and brassicas (brassica salad mix, baby tatsoi, thinnings of direct-sown brassicas, chopped young leaves of Tokyo bekana, Maruba Santoh or other Asian greens, mizuna, other ferny mustards such as Ruby Streaks, Golden Frills and Scarlet Frills). See Making salad mix
  • Microgreens: See Andrew Mefferd The Greenhouse and Hoophouse Grower’s Handbook.
  • When the weather warms up, consider using shadecloth for heat-sensitive plants, particularly lettuce, but any of the cool weather greens you still have by then.
  • In warm weather, greens and lettuces inside a tipi of pole beans will benefit from the shade.

Ways to Get More Crops from a Small Space

  • With transplants, you can fit more crops into each bed throughout the season, because each crop is occupying the bed for less time than if direct-sown.
  • Transplanting can help you grow more successions of summer crops, as each one needs less time in the garden or field.
  • Grow a vertical crop on a trellis and something short in the space below it. You can even use the same trellis twice, growing tomatoes after peas, for instance.
Spinach and peas in a relay planting scheme.
Photo Twin Oaks Community
  • Relay Planting is a method of growing short crops alongside taller ones. We have often sown peas down the center of a bed of overwintered spinach. As the peas grow tall, we trellis them, and continue harvesting the spinach. When the spinach bolts, we pull it up. This overlap of bed use lets us get more crops from a bed in less time than if we sowed the crops one after another. We have also sowed peanuts down the middle of a bed of lettuce on the same date we transplant the lettuce. We make sure to use vertical romaine lettuces rather than sprawly bibbs or leaf lettuces. We have transplanted okra down the middle of a bed of early cabbage. This does involve breaking off outer leaves of the cabbage if they are about to smother the okra.
  • Sow some slower-maturing crops the same time as you sow the fast ones, so you have food later as well as sooner! Carrots, turnips, cabbages, broccoli, collards, kohlrabi,
  • Sow some multiple-harvest crops to save work later. Greens that are harvested by the leaf, rather than the head, offer good value.

Sources for More Information

  • In High-Yield Vegetable Gardening, Colin McCrate and Brad Halm point out that when planning what to grow, it’s important to consider how long the crop will be in the ground, especially if you have limited space.
  • Cindy Conner in Grow a Sustainable Diet: Planning and Growing to Feed Ourselves and the Earth, leads you through the process of identifying suitable crops for food self-reliance, and provides a worksheet to help you determine Bed Crop Months. For each bed, determine how many months that food crop occupies that bed and so assess the productivity value of one crop compared with another. Short season crops grow to harvest size in 30-60 days, allowing series of crops to be grown in the space, and feeding people quickly. If all your nutrients are to come from your garden, you will need to pay attention to growing enough calories. Otherwise you’ll lack the energy to get to the end of the season!
  • Curtis Stone, in The Urban Farmer, distinguishes between Quick Crops (maturing in 60 days or less) and Steady Crops (slower maturing, perhaps harvested continuously over a period of time). He has designed a Crop Value Rating system based on 5 characteristics. To use this assessment, you look at each characteristic and decide if the particular crop gets a point for that characteristic or not. Then look for the crops with the highest number of points. Spinach gets all 5 points; cherry tomatoes only 3. The smaller your farm, the higher the crops need to score to get chosen. His 5 are:
  1. Shorter days to maturity (fast crops = chance to plant more; give a point for 60 days or less)
  2. High yield per linear foot (best value from the space; a point for1/2 pound/linear foot or more)
  3. Higher price per pound (other factors being equal, higher price = more income; a point for $4 or more per pound)
  4. Long harvest period (= more sales; point for a 4 month minimum)
  5. Popularity (high demand, low market saturation)
  • Steve Solomon in Gardening When it Counts provides tables of vegetable crops by the level of care they require. His Easy List: kale, collards, endives, chicories, spinach, cabbage, Irish potatoes, sweet potatoes, all cucurbits, beets, chard, sweet corn, all legumes, okra, tomatoes (followed by the more difficult eggplant, peppers).
  • See my blog post How to Decide Which Crops to Grow
  • See my article Intercropping: Minimize Your Effort While Maximizing Yields, in the Heirloom Gardener of Spring 2018.
  • Jennifer Poindexter on the Morning Chores Site has a nice simple web post on 16 Fast Growing Vegetables That Will Give You a Harvest Quickly
  • Steve Albert on the Harvest to Table website has a good post on Quick-Growing Vegetable Crops. It includes recommended fast-growing varieties of 29 crops.