Cold Hardy Crops & Season Extension

Cold Hardy Crops & Season Extension

Updated on Jun 14, 2019
By Shannon McCabe

Season Extension: Thriving in Winter

Shannon McCabe in her winter garden holding trays of plants

Some people see winter time gardening as a gambler's game. I prefer to look at it as an opportunity to experiment and learn how to work with the weather... not against it. My first foray into winter gardening was typical of a coastal New England farming experience, blustery and bitter; one of the coldest seasons on record! The farm I was working at was situated right on a salt pond and the cutting wind chapped your face and desiccated even the most vigorous plants. Battling the winter to eek out greens, carrots and beets felt, at times, like an insurmountable feat. However, those greens and roots were by far the most satisfying and intensely sweet veggies I have ever grown or eaten.

Aside from the pride and satisfaction of nurturing crops through an inhospitable winter, consider the other major benefits. Fresh vegetables are the cornerstone of a healthy diet, for those of us in cooler winter climates. Good-quality, fresh produce can be scarce in the off-season. Aside from the nutritional rewards, you will reap the emotional benefits of waking up a bit earlier and getting a burst of fresh air while tending to your winter garden. This extra bit of sunlight, fresh air and connection to the earth is an unbelievably uplifting gift you can give to yourself during an otherwise dreary season. I invite you to approach your winter gardening adventure as a chance to see what pleasant surprises and valuable lessons you can take away, rather than a risky roll of the dice.

two men wrapping plastic sheeting over frame to build hoop greenhouse

Season extension methods range from simple straw mulch and row covers, to cold frames and greenhouses. Choosing the best structure or method depends on your location, climate and needs. For a low maintenance and affordable beginner's project, consider low--tunnels. An ingenious concept introduced by Eliot Coleman, a Maine--based year round gardening expert, the low tunnel is essentially a mini greenhouse. Place wire or PVC hoops about every 3-4 feet along a 3 foot wide bed and cover with a floating row cover and a strip of greenhouse plastic. This temporary “greenhouse” will provide a temperature buffer as well as protection from cold drying winds. One of the best features of this simple design is that, while one side of the plastic remains buried and in place until spring, the other side of the bed is held down by bags of gravel, dirt or sand. The bags can be removed and this curtain of protection can be pulled back for easy harvesting access or to ventilate on unseasonably warm winter days. This design is ideal to push a late crop of cold hardy vegetables such as kale, collards, lettuce, hardy winter annual greens, beets, carrots and winter radishes. Low tunnels are also ideal for fall sowing early spring crops. Have you ever noticed that some of the “volunteer” seedlings, (those that self seeded in the previous year), tend to grow better than the same plants that you lovingly seeded in the ground at the recommended planting day? Planting in fall for a spring harvest, will allow for the seeds to germinate at the earliest possible time to ensure a super early crop. Try planting spinach in early October to harvest super--early the following spring, or plant peas and carrots in early November to germinate as soon as winter breaks.

cold frame shown on part of a raised garden bed

Are you more of a re-purpose or recycle- happy gardener? Or perhaps you have a small space, and are looking for a beautiful and functional structure? Cold frames are constructed out of re-purposed double pane windows and lumber. They are ideal for small gardens, you can also use cold frames to get an early jump on starting seedlings. Some cold frame designs can be as simple as placing a window over a basic rectangular frame. However, building a cold frame with a slope towards the winter sun is best. Attach the glass top with hinges to allow for easy access and to allow the window to be propped open for airflow in warm winter weather. Cold frames are not a new invention, they have been traditionally used for hardening off greenhouse transplants or to start seedlings early in the season, However cold frames are now commonly being used to grow cold--tolerant crops through the winter. This is ideal for kale, swiss chard, lettuce, collards, asian greens, beets, carrots, peas, and greens like corn salad, claytonia or arugula.

plants growing in raised beds inside a small hoop-style greenhouse

Unheated hoop houses and heated greenhouses can be a significant up front investment, however growing a large volume of produce to sustain you and your family for the winter will likely make up for the initial cost of the structure. Many people consider the greenhouse an oasis... an escape from the winter drudgery. It feels like cheating the weather! Unheated hoop houses are ideal for larger families or small market farmers. They have a low operating cost and can even be built on tracks to move the structure short distances. Given that unheated hoop houses are very similar to unheated low tunnels, the same crops can be grown in both; cold hardy greens and root crops as well as peas. Heated greenhouses can range from a small extension or enclosed porch on the back of your home, to a freestanding glass or plastic structure. With the addition of heat, the sky is the limit for greenhouse growing, except for those crops that are day length sensitive and will not fruit without the summer daylight hours or additional lighting. Some of the more interesting crops that thrive in greenhouses are ginger root, papaya and figs.

snowy landscape with greenhouse and woodpile. The greenhouse has a chimney and there are icicles on the eaves

While it can be thrilling to picture yourself harvesting tomatoes out of a greenhouse in wintertime, a good rule of thumb is to try to find crops that like the cold, rather than trying to fight the weather. Certain crops will tolerate cold temperatures and a few will really thrive in cold weather. Greens such as lettuce, spinach, kale, and arugula will all tolerate cool temperatures. The cold loving greens that cannot be beat for winter production are swiss chard, claytonia, (or miner's lettuce), collard greens, and mache. These greens only improve with cool weather, oftentimes with no more protection than a layer of straw mulch or a floating row cover, depending on what your climate is like. Some root crops taste best after being exposed to cool temperatures. This is so for carrots and beets. Sow them in late September up until mid November to harvest carrots in late Fall and in early Spring. Winter radishes are spicy and flavorful. They grow well in cold weather and they have a great storage quality. Peas love cool weather. Thomas Jefferson, who was a devoted gardener, was said to have participated in an annual competition with his neighbors to see who could grow and harvest the first peas of the season.

Perhaps the best part about winter gardening is that you've got nothing to lose! You will no doubt learn through this method of trial and error and the rewards are too tempting to pass up. Winter gardening has become a fast growing trend in the United States with the demand for local foods skyrocketing and Americans seriously considering food security as a critical element of homeland security. Consider this winter gardening learning experience as taking your part in becoming a more sustainable society. How many other measures of improving homeland security can be as simple as planting a seed? 

Shannon McCabe is a co-garden manager at the Baker Creek headquarters in Missouri. She studied Environmental Horticulture and Sustainable Agriculture at the University of Rhode Island. She was a market farmer in her hometown of Block Island, Rhode Island, as well as in Wakefield, Rhode Island.