“You can have a salad every night all winter long.” So says Eliot Coleman , New England’s guru of the four-season harvest. There’s no big secret. As long as there is ample daylight—and even in Coleman’s home of Harborside, Maine, there is ample daylight—you can use a variety of techniques for cold-weather gardening that will extend your growing season, effectively “moving” your garden beds 500 miles south.
From Yankee Magazine:
For more than 30 years, Eliot Coleman of Harborside, Maine, has successfully grown food in winter without heated greenhouses. Think outside your zone. Each winter, his gardens head south, to Georgia, without moving an inch.
How? For every layer of protection–a cold frame, for example–the growing environment shifts 500 miles. By doubling up, says Coleman, winter farmers never have to contend with frozen soil, not even when the mercury drops well below zero. “You might get a little surface freezing, but by 10 a.m. it will be unfrozen,” he says. “The minute the sun comes out, all of a sudden it’s 50 degrees in there. We’ve never had a day when we couldn’t put seeds in the greenhouse beds.”
For more on winter gardening, go to: Four Season Farm 
Coleman says you can find simple, inexpensive options out there to protect your plants. If you’re already using a cold frame, he recommends getting six unused 2x4s and building an A-frame around the structure, then wrapping the new enclosure in greenhouse plastic.
No cold frame? No problem. Coleman is also a big fan of “hoop houses,” small enclosures made from semicircle-shaped strips of metal or plastic piping covered in plastic. “I’ve been doing this a long time, and I’m still like a little kid when I go in there and see what’s happening,” he says. “It’s amazing that it just works.”