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).

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