by Karl H. Kazaks
With winter upon us, it’s time to plan for the upcoming year. If you’re so inclined (and aren’t already doing so already) consider using the colder months to extend your growing and harvesting season — even aim for year-round production.
Consumer hunger for locally grown produce doesn’t go away during the winter, so you won’t be lacking for buyers. What’s more, by having produce available in the winter, you’ll have a better chance of retaining your customer base during the warmer months, when there is more competition. Also, winter production can be a good way of keeping good employees.
When it comes to cold-hardy vegetables, Pam Dawling, author of Sustainable Market Farming and manager of a 3.5 acre garden that feeds a 100-person community in central Virginia, divides them into four broad categories.
There are the types of vegetables which are considered cool-weather crops but must be harvested before very cold weather sets in: most beets and cabbage, carrots, radishes, turnips, kohlrabi.
Then there are the root vegetables and greens which you can, depending on weather conditions, maintain well into winter: some types of cabbage and chard, some leeks, Asian winter radishes, Brussels sprouts. The seasons for many of these crops can be significantly extended with row cover. At a recent meeting in Charlottesville, VA Dawling mentioned that with row cover she was able to keep spinach thriving when temperatures drop to as low as 6 degrees F.
In the third category are winter-hardy crops which continue to flourish throughout the winter, providing multiple harvests. This group includes the best cold-hardy kale varieties (Dawling likes Vates) and some collard and leek varieties.
The final crops are the ones you overwinter for early spring-harvest crops: Tuscan kale, spinach, and purple sprouting broccoli, among others.
“In this region, planting a winter crop successfully means not jumping into it in August,” said Even’ Star Organic Farms’s Brett Grohsgal.
Grohsgal’s farm is in southern Maryland, near the Chesapeake Bay. The map shows it as zone 7, “but it’s feeling a lot like zone 6 this year,” he said. That’s because this winter began cold following what was a cold summer, so there’s no residual buffering warmth in the soil and ecosystem. Grohsgal plants his winter crops from Sept. 3 to Oct. 3.
Dawling looks in part to the germination of weeds like chickweed and henbit to help her decide when to sow winter crops. “It’s a kind of built-in signal,” she said.
With spinach, Dawling likes to start sowing about eight weeks before the date of first frost. Sometimes at that date the soil temperature is too warm for spinach. To circumvent warm soils, Dawling will germinate spinach in a refrigerator.
One method she has used is to sprout seeds in a jar. Since the sprouts won’t be used for direct consumption, you don’t have to worry too much about managing them. Upending the jar every day or so to allow the seed to get an even mix of air and moisture is advisable.
When removing the sprouts from the jar, use a dry, non-caking agent (like oats or grits) to separate the many sprouts, Dawling said. The whole procedure, she promised, “is really easy.”
When it comes to crops sown for early spring harvest, don’t try to push the envelope and plant early, aiming to get both a fall and an early spring crop. If a plant bolts in November or December, Grohsgal said, you won’t get that late winter/early spring crop you’d been planning for. Be patient and plant a little later.
Garlic is a perfect example of the benefits of patience. Dawling recommends garlic when the soil temperature at four inches is 50 degrees F. “If you plant them too warm, they can get too much top growth and get killed in the winter,” she said. “If you plant them too late, they won’t have enough root growth to survive the winter.”
When planting garlic, Dawling also plants what she calls garlic scallions. She takes the smallest garlic bulbs and plants them shoulder to shoulder in a furrow. In the spring she then harvests their young green shoots as scallions. They do taste mildly of garlic, but they are an early crop and so can help distinguish you in the marketplace.
Even’ Star has been producing year-round produce on a commercial scale since 1996. Though he does have two greenhouses, mostly for lettuce production, Grohsgal prefers field-grown vegetables. They have sweeter taste, he says. This year he has 24 acres of winter field production. The produce will be going to 225 CSA customers plus a number of wholesale accounts.
For over 20 years Grohsgal, who has a strong plant physiology background, has been developing seed especially for cold weather. (He also breeds for warmer weather). Currently he is working with about 15 cold hardy gene lines.
He is well-known as the source of Ice-Bred arugula. Having the winter hardy gene varieties has helped Grohsgal contend with the colder weather this year. His crops survived, he said, “almost unscathed.” Without the cold-tolerant lines, though, he added, “I’d be done.”
Climate is important when it comes to managing a winter grow program, but you’ve got to factor in more than just air temperature. “For winter cropping,” Grohsgal said, “soil drainage is really important.” Winter is a difficult time for most plants, so you don’t want to exacerbate their stress with waterlogged soils.
There are other advantages to growing in the winter, too. As Dawling pointed out, in the winter what weeds there are grow more slowly, and there is less pest pressure.
Usually in December Grohsgal is marketing a number of products. Some are stored from earlier in the year, such as sunchokes and fingerling potatoes. But much is still freshly harvested, produce a stir fry blend composed of greens from bigger-leafed brassica, Ice-Bred arugula, and a mesclun mix which for him comes about 3/4 from the field and 1/4 from greenhouse.
If you do grow leafy greens in a greenhouse in the winter, Dawling noted, know that due to slower rates of photosynthesis, they can have dangerously high levels of nitrates. Thus, she advised, don’t use animal-based fertilizers like bonemeal or feathermeal (which would compound the risk). Make sure to provide enough ventilation so plants will have enough carbon dioxide to permit photosynthesis (and flush out accumulated nitrates). Finally, don’t harvest on overcast days, and on sunny days don’t harvest until the plants have seen at least four hours of sunlight (six is better, she said).
There is plenty of opportunity in growing cold hardy crops for winter production, even in certain circumstances the possibility of year-round production. But it takes careful planning and using the right varieties.
“It’s pretty intense,” Grohsgal said. “It takes a lot to be able to crop for 12 months a year.”
Using hardy vegetables for winter growing: some expert opinion
by Karl H. Kazaks