Cold Frame Gardening

comments (6) August 13th, 2009

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Like most vegetable gardeners, I’ve always been interested in extending the har­­vest beyond the confines of “the growing season.” Along with the prolonged enjoyment of puttering in the garden, I treasure the reward of continuing to eat fresh, home-grown food. The easiest and most economical way to do this is with a cold frame.

If, like me, you’re not ready for the gardening year to end with the season’s first hard frost, then maybe you’re ready for a cold frame, too. This simple bottomless box with a removable glass or plastic lid protects plants inside from excessively low temperatures, wind, snow, and rain. In doing so, it creates a microclimate that is a zone and a half warmer than your garden. My garden may be in Maine, but the plants in my cold frame think they’re in New Jersey. A cold frame in New Jersey provides Georgia weather. The result is a harvest of fresh vegetables all winter long.

Why all this talk about winter crops when you’re still waiting for the first tomato? Because you can’t wait until winter to plant the winter garden. The rate that plants grow diminishes with the shortening days of fall until it almost stops. By then, the plants need to have reached harvestable size. After that, they’ll hibernate successfully in the shelter of the cold frame. I start sowing seeds in my cold frame mid-July (see A cold frame timetable), but that's because I live in Maine. You'll need to adjust your planting schedule for your local climate.

I began serious exploration of winter cold-frame gardening back in 1981 when I took the job of farm manager at a private school in Vermont. The program was supposed to supply the school with food while engaging students in a hands-on way. The problem was, there wasn’t much overlap of the gardening year and the school year. To involve students in fresh vegetable production, it would have to happen in winter. And if winter horticulture were to catch on with teenagers, it would need more charisma than a Brussels sprout. A large, heated greenhouse was out of the picture, and so I turned to cold frames.

Bottomless box with a skylight
The beauty of a cold frame is that it’s simple. Mine would have been familiar to a gardener a hundred years ago. Each one is a bottomless box made of 2-in. thick planks, 12 in. high at the back and 8 in. high at the front, and covered with glass frames, called lights.

	Download plans, a materials list, and instructions for building this cold frame.

The back of the frame is cut higher than the front so the angled lights can catch the slanting winter sun. I site the frames with the lights sloping toward the south in a spot where they will have as much winter sun as possible. Some shade is tolerable, but full sun is best.

If you have access to old storm windows, you can use those as lights. If you don’t want to build your own frame, however, you can buy a sturdy ready-made polycarbonate-glazed cold frame for a few hundred dollars (companies that sell cold frames include Charley's Greenhouse & Garden and Peaceful Valley Farm & Garden Supply).

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posted in: Projects, fall garden, greens, cold frame

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