Cold-Hardy Winter Vegetables

©Pam Dawling 2014 Twin Oaks Community, VirginiaAuthor of Sustainable Market Farming

Published by New Society Publishers

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pam@twinoaks.org

What’s in this presentation

• Why would you farm in winter?• Tables of cold-hardiness• Four ranges for cold-hardy crops• Examples of suitable crops• Scheduling outdoor crops• Hoophouse growing in winter• Storage• Resources• My contact info

Why grow winter vegetables?People eat all year long!Winter share CSAs are more in demand as the locavore movement grows, There is a year-round demand for local foods in stores and markets. Keep your customers,Keep your crew,Keep in shape!It’s easier than the summer - you have fewer crops to take care of,Weeds grow slower in colder weather, planting dates may become more flexible.

Before taking the plunge into winter gardening

know your climate, know your resources,know your market, know your crops (the main focus of this

presentation), when you don’t know, experiment on a small

scale.

Rowcover Wonderful rowcover : lightweight, easy to use, easy to store.

Edges need to be held down by bags of rocks or sand, plastic jugs of water, or metal or wooden stakes lying along the edges.

To protect against frost, you need a heavyweight rowcover. Thinner types are for protection from insects. Dupont Xavan 5131 (previously called Typar). 1.25 oz/sq

yd) fabric, can last for more than six years. Spunbonded polypropylene with UV stabilizers, 75% light transmission, and provides about 6 degrees F (3.3 degrees C) of frost protection.

We also use Agribon 17 (or 19), spun-bonded polypropylene 0.55 oz/sq yd, transmits 85% of sunlight, and offers 4°F (2.2°C) of frost protection for winter use.

We think polypropylene rowcover lasts longer and is tougher than polyester (Reemay).

Thinner rowcover can be used doubled up in severely cold weather, if you don’t have enough thick rowcover.

Photo credit Kathryn Simmons

Avoiding pitfalls of rowcover If you are growing on bare soil rather

than plastic mulch, weeds will grow very well, secretly and out of sight.

Rowcover reduces light levels. Ventilate covered crops in mild

weather, so they don’t lose their cold tolerance.

Hoops keep rowcover from sticking to frozen leaves and reduce abrasion. 9- or 10-gauge wire. In winter we use double wire hoops — the outer hoops trap the rowcover so it doesn’t blow away. The microclimate under hooped rowcovers is very pleasant in chilly, windy weather.

There are also spring steel hoops, for setting by machine or by hand. Easy to store - they return to a relaxed bow shape when removed from the soil, don’t get tangled. Seem to come in just one length, 64" (1.63 m), which is fine for a single row of plants, but less good for our 48" (1.2 m) beds with multiple rows.

Protection from pests For nursery seedbeds we use rowcover or ProtekNet (from Purple Mountain Organics) on wire hoops. Overly thick rowcover or rowcover resting directly on the plants can make the seedlings more likely to die of fungal diseases in hot weather — good airflow is vital. For transplanted crops, an 84" (2.1 m) width rowcover or mesh can form a tunnel over two crop rows 34” apart, giving good airflow.Photo credit Dubois Engineering

Winter Hardiness Table – Frosty Weather

Some starting numbers of killing temperatures, although your own experience with your soils, microclimates and rain levels may lead you to use different temperatures:• 35°F (2°C): Basil.• 32°F (0°C): Bush beans, cauliflower curds, corn, cowpeas, cucumbers,

eggplant, limas, melons, okra, some pak choy, peanuts, peppers, potato vines, squash vines, sweet potato vines, tomatoes.

• 27°F (–3°C): Some cabbage, Sugarloaf chicory (takes only light frosts), radicchio.

• 25°F (–4°C): Broccoli heads, chervil, chicory roots for chicons and hearts, Chinese Napa cabbage, dill, endive (hardier than lettuce, Escarole more frost-hardy than Frisée), annual fennel, large leaves of lettuce (protected hearts and small plants will survive even colder temperatures), some mustards and Asian greens (Maruba Santoh, mizuna, most pak choy, Tokyo Bekana), onion scallions.

Colder• 22°F (–6°C): Arugula, tatsoi (both may survive colder than this).• 20°F (–7°C): Some beets, cabbage heads (the insides may still be

good even if the outer leaves are damaged), celeriac, celtuce (stem lettuce), perhaps fennel, some mustards/Asian greens (Tendergreen, Tyfon Holland greens), radishes, turnips with mulch to protect them (Noir d’Hiver is the most cold-tolerant variety).

• 15°F (–9.5°C): Some beets (Albina Verduna, Lutz Winterkeeper), beet leaves, broccoli leaves, young cabbage, celery (Ventura) with rowcover, cilantro, endive, fava beans (Aquadulce Claudia), Russian kales, kohlrabi, Komatsuna, some lettuce, especially small and medium-sized plants (Marvel of Four Seasons, Rouge d’Hiver, Winter Density), parsley, Asian winter radish (including daikon), large leaves of broad leaf sorrel, turnip leaves, winter cress.

Colder still

• 12°F (–11°C): Some cabbage (January King, Savoy types), carrots (Danvers, Oxheart), most collards, some fava beans (not the tastiest ones), garlic tops if fairly large, most fall or summer varieties of leeks (Lincoln, King Richard), large tops of potato onions, Senposai, some turnips (Purple Top).

• 10°F (–12°C): Beets with rowcover, purple sprouting broccoli for spring harvest, Brussels sprouts, chard (green chard is hardier than multi-colored types), Deadon cabbage, some collards (Morris Heading), Belle Isle upland cress, some endive (Perfect, President), young stalks of bronze fennel, perhaps Komatsuna, some leeks (American Flag), Asian winter radish with mulch for protection (including daikon), rutabagas, (if mulched), large leaves of savoyed spinach (more hardy than flat leafed varieties), tatsoi.

Coldest

• 5°F (–15°C): Garlic tops if still small, some kale (Winterbor, Westland Winter, perhaps Blue Ridge), some leeks (Bulgarian Giant, Laura, Tadorna), some bulb onions (Walla Walla), potato onions and other multiplier onions, smaller leaves of savoyed spinach and broad leaf sorrel, a few unprotected lettuces if small (Winter Marvel, Tango, North Pole, Green Forest).

• 0°F (–18°C): Chives, some collards (Blue Max, Winner), corn salad, garlic, horseradish, Jerusalem artichokes, Vates kale (although some leaves may be too damaged to use), Even’ Star Ice-Bred Smooth Leaf kale, a few leeks (Alaska, Durabel), some onion scallions (Evergreen Winter Hardy White, White Lisbon), parsnips, salad burnet, salsify, some spinach (Bloomsdale Savoy, Olympia, Tyee).

Four situations1. Cool weather spring/fall crops to

harvest before very cold weather (see my slideshow Fall Vegetable Production for more on these crops)

2. Crops to keep alive as far into winter as possible

3. Hardy winter-harvest crops4. Overwinter early spring-harvest crops

1. Cool weather spring/fall crops to harvest before very cold weather

Some crops grow in spring and again in the fall –Asian greens, beets, broccoli, cabbage, carrots, chard, collards, kale,

kohlrabi, lettuce, peas, radishes, rutabagas, scallions, spinach, turnips.

Bed of young Danvers carrots.Credit Kathryn Simmons

2. Crops to keep alive as far into winter as possible

Many greens and roots can survive some freezing, so it is worth experimenting to find how late you can keep crops outdoors.Use the table to get an idea of what to expect. Celeriac takes 20°F (–7°C )Large Smooth Prague celeriac.Credit Southern Exposure Seed Exchange.

Broccoli and cabbageIt’s really worth growing fall brassicas because as they mature in the cooler fall days they develop delicious flavor. The most challenging part of growing fall brassicas is getting the seedlings growing well while the weather is hot. Unlike some cool-weather vegetables such as spinach, brassicas actually germinate very well at high temperatures: the ideal is 77°F–85°F (25°C–29°C), but up to 95°F (35°C) works. Weeds and pests slow down — once established these crops need little care.

Cabbage bed, credit McCune Porter

Lettuce

Heat-tolerant varieties also tolerate cold. There are also specialized cold-hardy varieties that do not tolerate heat (because they have a relatively low water content). Sow these in fall and winter only. Rowcover will provide a temperature gain of 4–6 degrees F (2.2–3.3 degrees C), depending on the thickness. It also reduces light transmission and airflow, but the trade-off can be very worthwhile. Lettuce may survive an occasional dip to 10°F (–12°C) with good rowcover — but not 8°F (–13°C), I can tell you! Adolescent lettuce are more cold-hardy than full-sized plants.

Lettuce varieties for fall and winterParticularly cold-hardy for outdoors: Brune d’Hiver Cocarde Esmeralda Galactic Green Forest Hyper Red Wave Kalura Lollo Rossa North Pole Outredgeous Rossimo Rouge d’Hiver Sunfire Tango Vulcan Winter Marvel

Rouge d’Hiver Lettuce Credit Southern Exposure Seed Exchange

The Salad Bowls are not so good outdoors in cold weather but do well under cover. Icebergs do not survive frost.

Cold-hardy Asian GreensTatsoi/tah tsoi • small, flat rosette of shiny, dark green

spoon-shaped leaves and white stems • Mild flavor, attractive appearance,

easy to grow• extremely cold tolerant, hardy to 22°F

(–6°C) or colder • Can direct sow and thin into salad

mixes, leaving some to mature at 10" (25 cm) across for cooking green.

• Can transplant at 6" (15 cm) • Kitazawa Seeds have a Red Violet

tatsoi, with an upright habit • Takes 21 days to become baby salads • 45 days to reach cooking size

Yukina Savoy • like a bigger tatsoi, with

blistered dark green leaves, greener stems and delicious flavor

• about 12“ (30 cm) tall • Both heat and cold tolerant • Can transplant at 12" (30 cm) • Needs 21 days to reach baby

size, 45 days to full sizeTatsoi, Yukina Savoy, Credit Ethan Hirsh

In spring the order of bolting of Asian greens is: tatsoi, pak choy, Komatsuna, mizuna, leaf radish, mustards.

Yukina Savoy Outdoors in DecemberAfter several nights at 16-17°F (-8 to -9°C)

More Cold-hardy Asian GreensKomatsuna - also known as mustard spinach and Summer Fest. Green or red, a large cold-tolerant plant 18" (45 cm) tall. Individual leaves can be picked and bunched, or the whole plant can be harvested. The flavor is much milder than the English name suggests. Baby salad size in 21 days, full size in 35 days;Senposai is quite heat and cold tolerant, a big plant with large, round, mid-green leaves. Usually harvested leaf-by-leaf. It can be very productive. Transplant it at 12"–18" (30–45 cm) spacing. Cooks quickly (much quicker than collards), and has a delicious sweet cabbagey flavor and tender texture. It is a cross between komatsuna and regular cabbage. It takes only 40 days to mature.Senposai. Photo Ethan Hirsh

Senposai in November – the young hoophouse crop is almost ready to take over

from the well-used outdoor crop.

Turnips and rutabagasRutabagas can be stored in the ground (unlike turnips, except in warm climates). Mulch over them with loose straw once the temperatures descend near 20°F (–7°C). Turnips do very well in the winter hoophouse. We also grow Purple Top White Globe outdoors in spring and fall.

White Egg turnip.Credit Southern Exposure Seed Exchange

3. Hardy winter-harvest crops

Deadon cabbageCredit Johnny’s Selected Seeds

Use the cold-hardiness table to look for crops that will survive your lowest temperatures, taking any crop protection into account. Add some wind protection, if you can. Look for the hardiest cultivars. At our Zone 7 farm, we overwinter Vates kale without rowcover, but not Winterbor or Russian kales. We grow our winter-harvest crops in our raised bed area, which is more accessible in winter and more suited to small quantities.

Favorite hardy winter-harvest crops – kale and spinach

We grow about 2800 row feet of overwinter Vates kale for 100 people and plant another 1000 feet in spring. We grow similar amounts of Tyee spinach.We use double hoops and rowcovers and pick spinach throughout the winter, whenever leaves are big enough. We pick one bed each day in October, November, February and March, when the weather is not too awful. Spinach makes some growth whenever the temperature is above about 40°F (5°C), so we can also make occasional harvests in December and January.

Vates kale Credit Kathryn Simmons

More cold-hardy winter-harvest crops

As well as kale and spinach, collards, leeks and parsnips also survive outdoors without rowcover at our farm (Zone 7). We grow only a few hundred feet of collards. We harvest small amounts throughout the winter, and when spring arrives, the plants give us big harvests sooner than the new spring-sown crops.Leeks and parsnips are slow growing, start them in spring.Lettuce can be grown outdoors with thick rowcover on hoops. We have also sometimes overwintered Danvers carrots and Deadon cabbage. Overwintered Vates kale

Winter-harvest leeksUnlike onions, leeks grow independently of day length and will stand in the field at temperatures below what many other vegetables can handle, increasing in size until you harvest them.Overwintered leeks.

Leek varieties - two main types: • the less hardy, faster-growing

varieties, often with lighter green leaves, which are not winter-hardy north of Zone 8,

• the blue-green hardier winter leeks. We like Tadorna (100 days), Jaune du Poiteau, King Sieg (84 days, a cross between King Richard and the winter-hardy Siegfried, from Fedco) and Bleu de Solaize (105 days, very hardy). Giant Musselburgh (105 days) is bolt-resistant, for overwintering in milder climates.

Other hardy winter-harvest crops• Small greens such as arugula, parsley, Belle Isle upland cress, winter

purslane, salad burnet and mache (corn salad) are very winter-hardy. • Some Asian greens are hardy. Best - Green in Snow mustard (Shi-Li-Hon)• Some unusual crops like horseradish, Jerusalem artichokes, salsify, and

some endive are hardy.• Walla Walla bulb onions and Evergreen Winter Hardy White or White Lisbon

scallions are surprisingly hardy.• Swiss chard is hardy to 15°F (–10°C) without rowcover. To keep chard

overwinter, either use hoops and rowcover (in mild areas, Zone 6 or warmer), or else cut off the leaves in early winter and mulch heavily right over the plants. It germinates best at 85°F (29°C) - useful as a substitute if the fall is too hot to sow spinach.

• Bright Lights chard. Credit Wren Vile

4. Overwinter early spring-harvest crops• spinach • kale, collards, cabbage • lettuce, chard • carrots• chicories such as radicchio and

Sugarloaf, • scallions, potato onions • garlic, garlic scallions. • In mild areas, peas can be fall sown

for a spring crop. Sow 1" (2.5 cm) apart to allow for extra losses.

Planting garlic. Credit Brittany Lewis

Some crops, if kept alive through the winter, will start to grow again with the least hint of spring weather and be harvestable earlier than spring plantings.

Garlic ScallionsSmall whole garlic plants. An attractive early crop. • Save small cloves from planting your main crop• Plant close together in furrows, dropping them

almost end to end, as they fall. Close the furrow and mulch over the top with spoiled hay or straw. • Plant next to your main garlic patch, or in a part of

the garden that's easily accessible in spring. • We harvest garlic scallions from early March till May,

at about 7-8" (18-20 cm) tall,• Trim the roots, rinse, bundle, set in a small bucket

with a little water, and you're done! • Scallions can be sold in small bunches of 3-6.• Some people cut the greens at 10" (25 cm) tall, and

bunch them, allowing cuts to be made every two or three weeks. We tried this, but prefer to simply pull the whole plant. The leaves keep in better condition if still attached to the clove. Photo Kathryn Simmons

Scheduling lettuce in fallThe short version on when to sow: • every 6-7 days in June and

July, • every 5 days in early August, • every 3 days in late August, • every other day until Sept 21. • every 3 days until the end of

September (for harvests through the winter).

Tango cold-hardy lettuceCredit Kathryn Simmons

Lettuce likes 40°F–80°F (4°C–27°C). Optimum 75°F (24°C) (germinates in only

2 days). Max germination temperature is 85°F

(29°C). Sow late afternoon or at nightfall - better

emergence than morning sowings.

Scheduling fall broccoli and cabbage We start sowing our fall brassicas for

outdoor planting around June 26 and repeat a week later for insurance -July 3

We use nursery seedbeds - Our rough formula is to sow around a foot (30 cm) of seed row for every 12'–15' (3.6–4.6 m) of transplanted crop row.

Last date for sowing these crops is about 3 months before the first fall frost date. In our case that means July 14–20.

Harvest– Cabbage from Sept 25 till late November. – Broccoli Sept 10–Oct 15, with smaller

amounts either side of those dates.

Broccoli transplant. Credit Kathryn Simmons

Kale: direct sown/transplanted mixOur mixed direct-sow/transplant method

allows for patchy germination, and requires less watering than if direct sowing it all.

Three times, (8/4, 8/10, 8/16), we sow two beds with rows 10" (25 cm) apart and then carefully thin them, leaving one plant every foot (30 cm)

We use the carefully dug thinnings from those beds to fill gaps and to plant other beds, at the same plant spacing.

Another reason we use this system is that we want a lot of kale, and there isn’t time to transplant it all.

Vates kale. Credit Kathryn Simmons

Scheduling Asian greensThe most cold hardy Asian greens can be harvested all winter in milder climates or kept alive until they revive in the spring to provide early harvests. Rowcovers on hoops will help keep them in marketable condition, and ameliorate the microclimate, for better growth rate. Wild Garden Seeds and Even’ Star Farm specialize in very cold-tolerant varieties. Hoophouses are the place to be in winter, if you are an Asian green. With the nighttime protection of two layers of plastic and an air gap, September sowings of these crops can thrive on the sunny days and grow at a surprisingly fast rate.

We start sowing our fall Asian greens for outdoor planting the same dates we sow fall broccoli and cabbage. The last date for sowing is about three months before the first fall frost date. In our case that means July 14–20.

Michihili cabbage. Credit Southern Exposure Seed Exchange

Scheduling hardy winter-harvest crops

• Slower-growing winter hardy crops like leeks and parsnips need sowing in late spring. We sow in March and April.

• Sow late cabbages (Deadon, Brunswick and January King ) in early summer. (Early June for us.)

Hollow Crown parsnips. Credit Southern Exposure Seed Exchange

Scheduling spinach• Optimum germination temperature for spinach is 70°F (21°C)

Max 85°F (29°C). Eight weeks before the first fall frost date is a good time to start planting spinach again, if it’s not too hot. Wait for soil temperature to drop (dead nettle, chickweed, henbit germinating). For earlier planting, pre-sprout seeds one week. We sow sprouted spinach 9/1 or so.

• 9/20-9/30 sowings over-winter small and make harvests in early spring. It grows every time air temperature tops 39°F (4°C).

Tyee spinach, our favorite variety. Credit Kathryn Simmons

Scheduling overwinter crops for early spring harvest

We sow one or two beds of spinach in late September, overwinter them as adolescents and harvest in the spring. These plants bolt later than the ones we harvest leaves from all winter, and earlier than spring-sown beds, so we get a continuous supply. Spinach, lettuce, chicories such as radicchio and Sugarloaf, fennel and cilantro seem to have the best cold tolerance when the plants go into winter half-grown. With alliums, such as bulb onions, multiplier onions and garlic, the harvest dates are regulated by day length, so the harvest cannot be earlier, but the bulbs will be bigger if you can overwinter the small plants.Garlic scallions are a great early spring crop – easy, flavorful, unusual.

When to plant garlic• Fall-planting is best. Garlic emerges quickly in the fall• 9 am soil temperature 50°F (10°C) at 4” (10 cm) deep. We plant

in early November. If the fall is unusually warm, wait a week. • Roots grow whenever the ground is not frozen• Tops grow whenever the temperature is above 40°F (4.5°C).

The hoophouse in winterWe are amazed at how incredibly productive hoophouses are. • Rate of growth of cold-weather crops is much faster inside• Crop quality, especially leafy greens, is superb. • Plants can tolerate lower temperatures than outdoors; they have

the pleasant daytime conditions in which to recover. Salad greens in a hoophouse can survive nights with outdoor lows of 14°F (–10°C).

• Working in winter inside a hoophouse is much more pleasant than dealing with frozen rowcovers and hoops outdoors.

• Greenhouses and coldframes also offer opportunities for cold-weather cropping, but get a hoophouse if you can.

Winter hoophouse crop overview• Salad crops • cooking greens • turnips • radishes • scallions• bare root transplants for setting

outdoors in February and March• We aim to harvest greens in the

hoophouse after the outdoor crops slow down, and turnips after the stored outdoor fall turnips have all been eaten, or as an occasional delectable alternative.

Fall outdoor sowings to transplant inside• Sept 15: about ten varieties of hardy leaf lettuce and

romaines, pak choy, Chinese cabbage, Yukina Savoy, Tokyo Bekana, Maruba Santoh, chard.

• Sept 24: Red and White Russian kales, another ten varieties of lettuce, Senposai, more Yukina Savoy, mizuna and arugula.

• We use hoops and ProtekNet, and water frequently.

Senposai. Credit Kathryn Simmons

Fall Hoophouse Planting - September Early September : We clear and add

compost to one of the beds and sow sprouted spinach seed, radishes, scallions, Bulls Blood beet greens and tatsoi.

Sept 15 and Sept 24: We make outdoor sowings of crops to later transplant into the hoophouse at 2–4 weeks old.

At the end of September we clear summer crops from one more bed, add compost and work it in. We transplant Tokyo Bekana and Maruba Santoh at 2 weeks old, Chinese cabbage, pak choy and Yukina Savoy at 3 weeks.

Photo November hoophouse beds. Ethan Hirsh

Fall Hoophouse Planting - October Oct 15 we sow our first turnips. (around our

first frost date) for harvest from Dec 4. We like Red Round and Hakurei and have tried out Oasis and White Egg to find a cheaper replacement for Hakurei (Oasis is the closest).

Our neighbor Gary Scott sows beet plugs in mid Oct, transplants them in the hoophouse and harvests from mid-March. Ace in 72 plug trays. He also loves a new variety from Johnny's called "Babybeat.”

Late October we sow more “filler” greens, baby lettuce mix, our second spinach, turnips and chard, and more radishes.

In the fourth week of October, we clear and prepare more beds and transplant the Senposai, mizuna, the 2nd lettuce, kale, arugula and Yukina Savoy at 4 weeks old.

Mizuna Photo credit Ethan Hirsh

Early October, we sow more radishes and some “filler” greens, (spinach, lettuce and Asian greens) to fill gaps later. We try hard to keep all the space occupied, mostly using lettuce and spinach. By mid-October we clear and prepare another bed and transplant lettuce at 10" (25 cm) apart, and chard.

Hoophouse Planting – November and December

Nov 10 we sow more turnips, mizuna and arugula, more filler lettuce and spinach, and our first bulb onions for field transplanting as early as possible in the new year.

Nov 11-20 we sow scallions, tatsoi, radishes, more bulb onion starts.

From Nov 10 on we aim to keep a fully planted hoophouse, and as each crop harvest winds down, we immediately replace that crop with another.

During December we use the “Filler” greens plants to replace casualties and heads of Chinese cabbage, Pak choy, Yukina Savoy each day as soon as we’ve harvested them. Pak Choy replacing Yukina Savoy here. Credit Ethan Hirsh

Daily hoophouse tasks in winter• Two hours work each day in winter in our 96’ x 30’ tunnel.• Keep the temperature in the 65°F–80°F (18°C–27°C) range during the day, opening

the big high windows, and the doors as needed. If the sun is shining we usually open the windows around 9 am and close them around 2:30 pm (a few hours before dark) to store some of the warmth.

• Even in cold weather, plants need fresh air! High-density cropping can really use up the carbon dioxide in a closed hoophouse very quickly. When this happens, photosynthesis crashes and plant growth becomes limited. Soil high in organic matter contains high levels of organisms that produce carbon dioxide. Dense plant canopies can trap this near soil level, where it is most useful.

• Our main task each day is harvesting. In the winter of 2009–2010, we had frozen soil or snow on the ground outside for a month (very unusual for us). Despite this we were able to keep a hundred people in fresh salad and cooking greens (with turnips and scallions for variety) for the whole month.

• Aside from harvesting, jobs include planting new crops, clearing old ones, spreading compost, hoeing, hand weeding and supplying water as needed.

• We have drip irrigation. In the middle of winter, not much water is needed, and we try to only water when a relatively mild night is forecast.

Persephone days and scheduling winter hoophouse crops

• When the daylight is shorter than 10 hours a day not much growth happens. It depends on your latitude.

• In Central Virginia, latitude 38° North, this period lasts two months, from November 21 to January 21. Soil temperature also matters. December 15-February 15 is the slowest growing time for us.

• To harvest in the darkest days of winter you’ll need to plan a good supply of mature crops to take you through. What has already grown before this period will provide most of your harvests.

• Be aware of the increase in days to maturity in winter. • For most of the winter, our hoophouse plants are actively growing, not merely

being stored for harvest (as happens in colder climate zones and outdoors), so we can continue sowing new hoophouse crops even in December.

Nitrate accumulation

• During periods of short daylight length, there is a health risk associated with nitrate accumulation in leafy greens. Nitrates are converted in the body into toxic nitrites, which reduce the blood’s capacity to carry oxygen. Also, nitrites can form carcinogenic nitrosamines.

• Plants make nitrates during the night, and convert them into leaf material during the day. It takes about six hours of sunlight to use up a night’s worth of nitrates. In winter, a small handful of leafy vegetables can exceed the acceptable daily intake level of nitrate for an adult, unless special efforts have been made to reduce the levels.

• Spinach, mustard greens and collards contain about twice as much as lettuce; radishes, kale and beets often have two and a half times as much. Turnip greens are especially high, at 3 times lettuce levels.

To keep nitrate levels as low as possible: Grow varieties best suited for winter; Avoid fertilizing with blood meal or feather meal; use organic compost. Ensure soil has sufficient P, K, Mg and Mo Water enough but not excessively; Provide fresh air as soon as temperatures reach 68°F (20°C), so that

carbon dioxide levels are high enough; Harvest after at least four (preferably six) hours of bright sunlight in

winter; Avoid harvesting on very overcast days; Avoid over-mature crops and discard the outer leaves. Harvest crops a

little under-mature, rather than over-mature; Use crops soon after harvest; Refrigerate immediately after harvest, store harvested greens at

temperatures close to freezing; Mix your salads; don’t just eat spinach.

Winter Vegetable Storage

Winter Squash storage• Meeting the different storage requirements of

various crops helps maximize their season of availability

• Many crops may be stored without electricity, perhaps in buildings that serve other uses at the height of the growing season.

• A publication from Washington State University Extension, Storing Vegetables and Fruits at Home, is a good introduction to alternatives to refrigerated storage, using pits, clamps and root cellars. There is also good information in USDA Agriculture Handbook 66.

• Some vegetables need to cure before storage and the curing conditions are different from those needed for storage. Curing allows skins to harden and some of the starches to convert to sugars.

Four Sets of Storage Conditions In my chart on the next slide, the Summary column indicates the general conditions needed for each crop, and allocates each crop to one of 4 groups: A= Cold and Moist : 32°F–40°F (0°C–5°C), 80%–95% humidity — refrigerator or winter root cellar conditions. Most roots, greens, leeks

B= Cool and Fairly Moist: 40°F–50°F (5°C–10°C), 85%–90% humidity — root cellar. Potatoes

C= Cool and Dry: 32°F–50°F (0°C–10°C), 60%–70% humidity — cooler basements and barns. Garlic and onions

D= Warm and Dry to Fairly Moist: 50°F–60°F (10°C–15°C), 60%–70% humidity — basements. Sweet potatoes and winter squash.

By providing storage spaces with these 4 types of conditions, 25 crops can be stored.

Table of Storage ConditionsSee the handout or my book Sustainable Market Farming, for the complete chart

In-ground storage Depending on the severity of your winter temperatures, some cold-hardy root

crops (such as turnips, rutabagas, carrots, parsnips, Jerusalem artichokes and horseradish) and also leeks can be left in place in the ground, with about a foot (30 cm) of insulation (such as straw, dry leaves, chopped corn stalks, or wood shavings) added after the soil temperature drops to “refrigerator temperatures.”

Hooped rowcovers or polyethylene low tunnels can keep the worst of the weather off. There could be some losses to rodents, so experiment on a small scale the first winter to see what works for you. We have too many voles to do this with carrots or turnips on our farm, but horseradish survives without protection, as do some winter-hardy leek varieties.

Besides being used as a method for storage of hardy crops deep into winter, this can be a useful method of season extension into early winter for less hardy crops such as beets, celery and cabbage, which would not survive all-winter storage this way. Access to crops stored in the ground is limited in colder regions — plan to remove them all before the soil becomes frozen, or else wait for a thaw.

Drawing credit WSU Storing Vegetables and Fruits at Home

Storage clamps (mounds)Cabbage, kohlrabi, turnips, rutabagas, carrots, parsnips, horseradish, Jerusalem artichokes, salsify and winter radishes (and any root vegetables that can survive cold temperatures) can be stored with no electricity use at all, by making temporary insulated outdoor storage mounds (clamps). • Mark out a circular or oval pad of soil, lay down some straw or other insulation, pile the

roots up in a rounded cone or ridge shape, and cover them with straw and then with soil, making a drainage ditch round the pile. As a chimney for ventilation, leave a tuft of straw poking out the center. Slap the soil in place to protect the straw and shed rainwater.

• For the backyarder, various roots can be mixed, or sections of the clamp can be for different crops. Those growing on a large scale would probably want a separate clamp for each crop. It is possible to open one end of a clamp or pit, remove some vegetables, then reseal it, although it takes some care for it to be successful.

• There is a balance to be found between the thermal buffering of one large clamp and the reduced risk of rot that numerous smaller clamps provide.

Drawing credit WSU Storing Vegetables and Fruits at Home

Pits and trenches• To store in pits or trenches dig a hole in the ground first, lining it

with straw, lay in the vegetables, then cover with more straw and soil. To deter rodents, it is possible to bury large bins such as (clean) metal trash cans, layer the vegetables inside with straw, and cover the lid with a mound of more insulation and soil. Trenches can have sidewalls made with boards to extend the height.

• Another alternative is to bury insulated boxes in the ground inside a dirt-floored shed or breezeway. A new life for discarded chest freezers! Insulated boxes stored in unheated areas need six to eight inches (15–20 cm) of insulation on the bottom, sides and top.

Drawing credit WSU Storing Vegetables and Fruits at Home

Root Cellars• A sustainable alternative to refrigerated storage for crops

needing cool, damp conditions. With a good in-ground root cellar, potatoes can be stored for five to eight months.

• Potatoes are best stored in a moist, completely dark cellar, ideally at 40°F (5°C), up to 50°F (10°C). Ventilate as needed during times of cool temperatures, to maintain the cellar in the ideal range.

• Below 40°F (5°C) the starches start to convert to sugars, giving the potatoes an unpleasant flavor and causing them to blacken if fried.

• Also for apples, cabbage, or root vegetables, but be careful what you mix, because ethylene from the apples, for example, will cause potatoes to sprout! Most other root crops can also be stored in a root cellar. Some people pack the unwashed vegetables in boxes of sand, wood ash, sawdust or wood chips. Perforated plastic bags are a modern alternative. Whole pepper plants with unripe peppers can be hung upside down in the cellar to ripen, or simply to store. Headed greens like cabbage can also be hung upside down, or be replanted side by side in boxes or tubs of soil. Celery and leeks can also be stored by replanting in the same way.

• See Nancy and Mike Bubel’s book Root Cellaring for construction details and advice

Twin Oaks root cellar. Credit McCune Porter

EthyleneEthylene is generally associated with ripening, sprouting and rotting. Some crops produce ethylene gas while in storage — apples, cantaloupes and ripening tomatoes all produce higher than average amounts. Environmental stresses such as chilling, wounding and pathogen attack can all induce ethylene formation in damaged crops. Some crops, including most cut greens, are not very sensitive to ethylene and so can be stored in the same space as ethylene-producing crops. Other vegetables, however, are very sensitive to the gas and will deteriorate in a high-ethylene environment. Potatoes will sprout, ripe fruits will go over the top, carrots lose their sweetness and become bitter. Drawing credit WSU Storing Vegetables and Fruits at Home

Resources – GeneralATTRA attra.ncat.org: Market Farming: A Start-up Guide, Scheduling Vegetable Plantings for a Continuous Harvest, Season Extension Techniques for Market Farmers. SARE www.sare.org A searchable database of research findings: Season Extension Topic Room Washington State University Extension, Storing Vegetables and Fruits at

Home pubs.wsu.edu/ListItems.aspx?Keyword=EB1326E USDA Agriculture Handbook 66 ba.ars.usda.gov/hb66/contents.html Virginia Co-operative Extension Service Fall Planting Guide

pubs.ext.vt.edu/426/426-334/426-334.html extension.org/organic_production The organic agriculture community

with eXtension. Publications, webinars, videos, trainings and support. An expanding, accessible source of reliable information.

Growing Small Farms: growingsmallfarms.ces.ncsu.edu/ Debbie Roos keeps this site up to the minute. Click Farmer Resources,

Resources - slideshowsMany of my presentations are available at www.Slideshare.net. Search for Pam Dawling. Cold-hardy Winter Vegetables Crop Planning for Sustainable Vegetable Production Crop Rotations Fall Vegetable Production Feed the Soil Growing Great Garlic Intensive Vegetable Production on a Small Scale Producing Asian Greens Succession Planting for Continuous Vegetable Harvests Sustainable Farming Practices Other slide shows I recommend: Mark Cain Planning for Your CSA: www.Slideshare.net (search for Crop Planning) Tom Peterson Farm Planning for a Full Market Season

vabf.files.wordpress.com/2013/02/tom-peterson-farm-planning-for-a-full-market-season.pdf

Brad Burgefurd, Cultural Practices And Cultivar Selections for Commercial Vegetable Growers. www.slideshare.net/guest6e1a8d60/vegetable-cultural-practices-and-variety-selection

Resources – books and seeds The Complete Know and Grow Vegetables, J K A Bleasdale, P J Salter et al. Knott’s Handbook for Vegetable Growers, Maynard and Hochmuth The New Seed Starter’s Handbook, Nancy Bubel, Rodale Books The Organic Farmer’s Business Handbook, Richard Wiswall, Chelsea Green Sustainable Vegetable Production from Start-up to Market, Vern Grubinger, The New Organic Grower, Eliot Coleman, Chelsea Green Extending the Season: Six Strategies for Improving Cash Flow Year-Round on the

Market Farm a free e-book for online subscribers to Growing for Market magazine Gardening When it Counts, Steve Solomon Grow a Sustainable Diet: Planning and Growing to Feed Ourselves and the Earth,

Cindy Conner, New Society Publishers Crop Planning for Organic Vegetable Growers, Daniel Brisebois and Frédéric

Thériault (Canadian Organic Growers www.cog.ca) Growing Great Garlic, Ron Engeland, 1991, Filaree Wild Garden Seeds www.wildgardenseed.com Even ‘Star Farm

http://www.localharvest.org/even-star-organic-farm-M9994 specialize in cold-tolerant varieties.

Cold-Hardy Winter Vegetables

©Pam Dawling 2014Twin Oaks Community, VirginiaAuthor of Sustainable Market Farming

Published by New Society Publishers

SustainableMarketFarming.comfacebook.com/SustainableMarketFarming

pam@twinoaks.org