Many vegetables prefer cooler temperatures and some even thrive through a cold snap. It is helpful to know how much cold weather is expected in your U.S. Department of Agriculture plant hardiness zone before planning for winter crops. The USDA recommends the use of portable mini-greenhouses called "hoop houses" to lengthen the growing season and improve soil fertility. Heavier mulching for winter plants also adds fertility to the soil and retains warmth. With protection in place, there are many types of vegetables that grow easily in winter.
Swiss chard planted in late August can begin to be harvested in 60 days and grows throughout the winter. When the plants are 8 inches tall the outer leaves can be removed for use. New leaves grow from the center of the plant. All varieties of greens, including lettuce, grow better during cool seasons--their seeds germinate best at 55 to 60 degrees F. Other salad greens that over-winter and can be harvested successively are radicchio, butterhead lettuce and arugula. In colder climates, mulch fall-sown salad greens with a thick layer of leaves after the first frost. According to University of New Hampshire Extension, they will spring back to life as soon as weather starts to warm and the mulch is removed.
Carrots, beets, parsnips, rutabagas, and turnips mature in 60 to 90 days, so plan the sowing time to coincide with frost dates. In mild-winter areas these crops can be grown year round. Root vegetables can tolerate cold weather better if they are well mulched and can be harvested as needed, according to Washington State University Extension. Radishes can also be harvested all winter long. Some radish varieties are table-ready in 20 days. Turnips are another vegetable that matures quickly and thrives in the winter garden. Experienced gardeners say turnips become sweeter after the first frost.
Cole and Cabbage
Broccoli prefers cool weather and if planted by mid-August it will be ready by Thanksgiving. Purple or Italian sprouting broccoli grows all winter. Another member of the cole family is Brussels sprouts. It has a slightly longer growing season than broccoli, but if planted by mid-July it will be ready in the fall. In mild areas Brussels sprouts over-winter easily, according to WSU Extension. The cabbage family includes family varieties such as Savoy and Chinese cabbage. Protect these plants with heavy mulch through very cold weather and they will produce food all winter. University of New Hampshire Extension advises cutting heads of cabbage in the fall and mulching the stumps--fist-size cabbages will sprout around the stumps as soon as weather begins to warm.