Vegetable Garden Tips

 

Young Yukina Savoy plants.
Photo Ethan Hirsh

My virtual workshop on Asian Greens 

is available from Mother Earth News Fairs Online here.

The Food Independence Course Part Two  consists of eight video presentations, most of which come with pdf handouts. My contribution is Growing Asian Greens, and pairs nicely with the Guide to Asian Vegetables by Wendy Kiang-Spray, author of The Chinese Kitchen Garden: Growing Techniques and Family Recipes from a Classic Cuisine. Other topics include Dandelion Wine, Homemade Teas, Food Conversations, Passive Solar Greenhouse Design, Productive Growing from Home, and Growing Your Own Spices.

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Decoy Cabbage White Butterflies.
Photo Good Seed Co

Easy DIY Cabbage Butterfly Decoy!

The Good Seed Co blog posted this lovely idea for protecting brassicas from those white butterflies Pieris rapae. It’s based on the discovery that the butterfly is territorial. If it sees a slightly bigger competitor it flies away. I have not tested this system, but it sounds like an interesting and fun project that costs next to nothing.

http://goodseedco.net/blog/posts/cabbage-butterfly-decoy Posted 25th Jun, 2015 in On Our Mind by Robin Kelson

PageOfCabbageMoths_efile

Cut out paper decoy representations of the butterfly. Here’s a single page template you can download

We don’t have many cabbage butterflies  because we have both a predator – the paper wasp, and a parasite –  Cotesia glomerata, a parasitic wasp that lays its eggs in small (first instar) larvae of the Cabbage White Butterfly, or Imported Cabbage Worm (as we call it in the US). Cotesia larvae emerge from the caterpillars after 15-20 days and spin yellow or white cocoons on or near the host which dies when the wasps emerge. We often find clusters of these cocoons (about the size of cooked rice grains) on the underside of brassica leaves.

I learned from Bryan O’Hara in  No-Till Intensive Vegetable Culture that our friends, the Cotesia glomerata wasps that parasitize brassica caterpillars, and overwinter as pupal cocoons on the undersides of brassica leaves, will hatch out in spring on the very day the overwintered brassicas start to flower. The 20-50 day lifecycle needs brassica flowers, so don’t be in a hurry to cut down all your bolting greens! The flowers provide nectar for the adult wasps. The leaves, as we know, provide food for the caterpillars, which provide the host for the wasps to lay eggs in. The wasp larvae feed on the caterpillar until it dies, then pupate.

There’s an incredible National Geographic video of this cycle, showing parasitic wasp larvae swimming around inside a caterpillar, bursting out through its skin. The weirdest bit is that it is the dying caterpillar that spins the protective cocoons around the pupating larvae. And us who plant the brassicas that feed the caterpillars! Who is the farmer and who is farmed?

This video shows a paper wasp tackling a caterpillar.

This one shows Cotesia glomerata emerging

This one shows more about the parasitic Cotesia glomerata 


Savoy cabbage with frost. Savoys can take much colder temperatures than this!
Photo Lori Katz

Average First and Last Frost Dates

Harvest to Table has this helpful article:

Average First and Last Frost Dates for Cities, States, and Countries

Average frost dates – the last one in spring and the first one in the fall – are useful to know when planning your crops. Once you’ve calculated your planting out date for various crops, you can work back to set sowing dates for the crops you’ll transplant, and bed prep dates for every crop. You can also make a co-ordinated plan that paces the work and doesn’t have too much in any one week, or any while you plan to be on vacation. You can calculate your first sensible planting date for each crop, your last one and perhaps some in-between ones to keep up supplies throughout the season.

You can use your average first fall frost date to make sure you don’t plant frost-tender crops too late in the season when you have no hope of them maturing in time for a harvest. You can extrapolate beyond the frost date to figure out when to harvest the more hardy crops. See my Winter-Kill Temperatures chart for useful tips.

By looking at the number of frost-free days in your area you can see whether to grow long-season tender crops like watermelons, or whether it’s only worthwhile if you choose fast-maturing varieties.

The Harvest to Table website is a trove of clearly explained information.

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Soil thermometer with easy-to-spot backing in a bed of beets.
Photo Bridget Aleshire

Soil Temperatures

Average frosts are only averages. Actual frosts can sometimes happen two weeks either side of those dates. Frosts are only one particular temperature, and may not matter to the crop you’re planning for. Soil temperatures for germination and for planting are another important part of planning.

K-State Extension has a brief article on the importance of measuring your soil temperature.

The Empress of Dirt has a helpful list of Best Soil Temperatures for Sowing Vegetable Seeds, in alphabetical order by crop.

Harvest to Table also has a list, ranked by temperature, so you can see what you can plant this week.

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Scottish Climate Friendly Farming Video

Farmer Patrick Barbour, from Highland Perthshire, has won the search for Scotland’s climate friendly farming champion. Patrick’s innovative three-minute video entry, filmed at Mains of Fincastle, near Pitlochry stunningly illustrates the benefits of tree planting, species rich grassland, rotational grazing for cattle and sheep and stitching nitrogen fixing crops into pastures.  It is available to watch at: Next Generation Climate Change Competition

Patrick, Robert and Catherine Barbour of Mains of Fincastle, near Pitlochry
Photo The Scottish Farmer

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.

Goodbye winter, hello summer!

Rhubarb season is almost here. Credit Kathryn Simmons
Rhubarb season is almost here.
Credit Kathryn Simmons

Spring in Virginia is so variable in temperature! But this year is more so than usual. We’ve just had three days with high temperatures of 90F (31C) or more. Not so long ago we had night-time lows of 20F (-6.5C). Late February and all of March was full of snow and rain.

The only thing we managed to plant in the garden for the whole of March was a small amount of shallot bulbs. We’ve been doing an impressive amount of scrambling in the first ten days of April, to make up for lost time. Some crops we had to cut back on, because it got too late to plant. We only have a quarter of the onions we planned, half of the peas, a fifth of the spinach, and no fava beans this year. I realize it would be useful to have “last worthwhile planting dates” for all our spring crops, to help decision-making.

To add insult to injury, a Beast ate half of our early broccoli transplants in the cold-frame one night. Because there were big surface tunnels, I think it was Eastern Moles. They are insectivorous, not vegetarian, but they do use leaves to line their nests, which they make at this time of year. I bought a trap – no luck. I covered the remaining broccoli and lettuce flats as best I could with rat wire “lids” and clear plastic domed food covers – things I had handy from previous depredations. What seems to have worked is to line the coldframes with landscape fabric and set the flats on that, tightly up against the edges, leaving no wiggle room. Wisely, we do a later, third, sowing of broccoli to cover emergencies, so we spotted those out into bigger flats. We’re going to need them this year.

Chitting seed potatoes ready for planting. Credit Kati Folger
Chitting seed potatoes ready for planting.
Credit Kati Falger
Newly emerging potato plant in the spring Credit Kathryn Simmons
Newly emerging potato plant in the spring
Credit Kathryn Simmons

We have at last got our potatoes in the ground, three weeks later than ideal. On the positive side, they had been chitting (green-sprouting) in crates under lights in the basement since the beginning of March, so I could console myself that they were growing anyway. And probably they will come up quicker in the (suddenly!) warmer soil. We cut them for planting once the area was disked for planting and we were pretty sure we could get them in the ground in a few days.

We’ve busily transplanted spinach, kale, lettuce and scallions, and sowed carrots, more scallions and the third bed of beets. We used the Earthway seeder for the beets, and found the radish plate worked better than the beet plate for Cylindra seed, which were smaller than the Detroit Dark Red. We also tried the popcorn plate with some success, when the beet plate jammed.

We flamed one of our first two beds of beets, to kill the weeds that didn’t die properly with our hasty delayed rototilling. We would have flamed both, but the Cylindra popped up overnight earlier than I expected (going by soil temperature), so we’ll have to hoe those really soon, maybe this afternoon.

Spring bed of cabbages planted into rolled hay mulch. Credit Kathryn Simmons
Spring bed of cabbages planted into rolled hay mulch.
Credit Kathryn Simmons

Next we’ll be prepping our cabbage and broccoli beds. We make temporary raised beds, roll out round hay bales over them, then transplant into the mulch. We do this by first measuring and making “nests”, using our hands to open up the mulch down to the soil. The brassicas appreciate the mulch to moderate the soil temperature and keep some moisture in the soil.

Our big weeding projects have been the raspberries and the garlic.(Goodbye, henbit!)

 

Mar 2013 Growing for Market
Mar 2013 Growing for Market

Today we might sow our parsnips. I just wrote an article about them in the March issue of  Growing for Market. This issue also contains articles about increasing hoophouse tomato production, adding solar panels, equipment for tracking the weather, food safety and new interesting cut flowers.

Florence bulb fennel. Credit Southern Exposure Seed Exchange
Florence bulb fennel.
Credit Southern Exposure Seed Exchange

The April issue is also out. For that, I wrote about fennel – bulbs, leaves, seeds and pollen. Other articles include one about Johnny’s Salanova lettuce, others about training cucumbers and tomatoes up strings in the hoophouse, a tractor implement for rolling out round hay bales (which is only fun to do by hand the first ten times, max), more on food safety, and an interview/field trip to Texas Specialty Cut Flowers. 

GFM-April 2013-cover-300px

Starting sweet potato slips

Growing sweet potato slips from roots planted in flats of compost.Credit Kathryn Simmons
Growing sweet potato slips from roots planted in flats of compost.
Credit Kathryn Simmons

The weather outside is still full of rain, but I’m optimistically starting growing our own sweet potato slips. Surely it will dry out by May?

Sweet potatoes are related to morning glory, in the genus Ipomoea. They are not yams, even though they are often called yams! True yams are a tropical species of tuber (genus Dioscorea). Sweet potatoes are roots, not tubers, and will not even cross with yams. So forget yams. Unlike white potatoes, which have the annual plant sequence of vegetative
growth, flowering and dying back, sweet potato plants would continue growing forever if the weather was warm enough.

The mystique of sweet potato slips

Sweet potatoes are not grown from seed or from replanted roots, but from “slips,” which are pieces of stem with a few leaves, grown from a mother root. We used to buy bare-root sweet potato slips to plant, believing growing our own would be very tricky. The collapse of our supplier and our desire to have organic plants (plus a need to reduce our expenses one year), pushed us into growing our own. We had some problems initially, so I can warn you about how not to do it. Now we have a system we really like, and we’ve found several advantages of homegrown slips over purchased ones.

With purchased slips, we had to specify a shipping date months ahead, then hope the weather sprites would be kind. We had to jump to when the plants arrived, and get them all in the ground pronto, to keep them alive as best we could (because their roots needed moisture). We accepted as normal a certain amount of drooping. We can have late frosts, spring droughts or El Niño wet springs, and climate change is only adding to the uncertainty. With homegrown slips we can delay planting if that seems wise; we can plant them in stages rather than all on one day. The transplants don’t wilt. We can grow them big and plant them with three to five nodes underground, giving more chance of survival in heat or frost. We can keep some spares on hand to replace casualties. The sturdy plants get off to a strong start, which could be an even bigger advantage further north where the season of warm-enough weather is on the short side for a 90–120-day plant. And we are self-reliant — we never have to spend money on them.

Timing

Figure out your ideal planting date and work back to find your starting date. Planting is usually done about two weeks after the last frost. The soil temperature should reach at least 65°F (18°C) at 4″ (10 cm) deep on four consecutive days. For us, that’s around May 12. It takes eight weeks to grow the slips, and the roots produce more slips if conditioned for two weeks (or even four), before you start to grow slips. So start ten to twelve weeks before your planting date. We now start March 1. Here’s where I made my first big mistake — following directions written for much further south, I tried to start growing slips in mid-January. Dismal fight against nature!

Testing (Optional)

If you want to get the best yields from your mother roots, first test the roots in a bucket of water — the ones that float are said to yield better and produce better-flavored roots. Next, test for viral streaking — also known as color breaks or chimeras, where paler spots or radial streaks appear in the flesh — and discard roots with pale spots or streaks wider than a pencil lead. Cut a thin slice from the distal end of each root — the stringy root end, opposite the end that was attached to the plant stem. All the sprouts will grow from the stem end, so don’t cut there! If you can’t tell the difference between the ends, you can ignore this step and plan not to propagate your own slips for more than a couple of years (so the virus load doesn’t get too high). Or if you are a home gardener dealing with a small crop, you could keep the slips from each root separately and cut up the mother root before planting and then discard the slips from streaked roots.

Conditioning (Also Optional)

Put the chosen roots in flats, boxes or trays, without soil, in a warm, moist, light place for two to four weeks. Ideal conditions are 75°F–85°F (24°C–29°C) at 95% humidity. This can double or triple the number of sprouts the root will produce in a timely manner. We use our germinating chamber, which is an old glass door refrigerator heated by a light bulb. See the photo above. Conditioning after testing allows the cut surfaces to heal before they are covered by compost. The environment for sprouting the roots is similar, so you can probably use the same location.

Sprouting

Set up a place with light, humidity and ventilation at 75°F–85°F (24°C—29°C) and with about 12″ (30 cm) of headroom. Plant the selected roots almost touching each other, horizontally in free-draining light potting compost in flats or crates. Water the boxes and put them to sprout. Once again, we use our ex-fridge germinator. Using boxes is much more manageable than having the roots loose in a big coldframe. Indoor spaces are much easier to heat than the great outdoors! Boxes can be insulated and put on a bench at a decent working height, with lights or heat lamps over them. Keep the compost damp, and if your planting medium is without nutrients, give liquid feed occasionally once sprouting starts. For small quantities of slips, it is possible to sprout the potatoes half-submerged in water, either in trays of water or by suspending a sweet potato impaled on toothpicks, resting on the top of a glass of water. For larger quantities I recommend our method.

Cut sweet potato slips put in water to grow roots.Credit Kathryn Simmons
Cut sweet potato slips put in water to grow roots.
Credit Kathryn Simmons

Cutting and spotting the slips
After 5–7 days, the roots will begin to produce slips. Ideally, wait until the slips are 6″–12″ (15–30 cm) tall with 4–6 leaves beginning, then cut them from the root and stand them in water. If necessary, cut them a bit shorter. Some people pull or twist the slips from the roots, but this could transfer diseases by bringing a small piece of the root with the sprout. I cut the slips daily, bunch them in a rubber band and stand them in a small bucket of water. The slips will grow more roots while they are in water for several days, which seems to be an advantage. Once a week I spot (plant) the oldest, most vigorous slips (with good roots) into 4″ (10-cm) deep wood flats filled with compost. The spotted flats require good light in a frost-free greenhouse and sufficient water. If you are two weeks away from your planting date and are short of slips, you can take cuttings from the first flats of slips that were spotted, to make more. The slips planted in flats become very sturdy, allowing flexibility about planting dates and a longer slip-cutting season. About ten days before planting, start to harden off the flats of slips by reducing the temperature and increasing the airflow. It’s also possible to skip the spotting stage and transplant the slips outside directly from the water, but I don’t think this is as good as spotting them into flats of good compost for a few weeks.

Once a week we plant the rooted slips in flats.Credit: Kathryn Simmons.
Once a week we plant the rooted slips in flats.
Credit: Kathryn Simmons.

From Sustainable Market Farming, (c) Pam Dawling, New Society Publishers 2013