Extending The Season

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You'll need to devise some way to open the windows. You can either hinge them in the back or—as we did—build channels for the units so you can slide them up and down (which gives finer ventilation control). In addition, you may want to lay down pliable weather stripping where the glazing meets the sides of your frame to help seal that junction.

Up to a certain point, plants double their growth rate for every 10°F rise in soil temperature, so anything you do to help keep the ground warm is going to pay off. For starters, insulate the sides of the frame with some closed-cell foam board . . . or simply pile hay or even soil around it.

You can further improve the frame's thermal performance by adding some heat-retaining mass to it. If you insulated the foundation, you're effectively using the interior soil itself as thermal mass. You can also stack 30-gallon water-filled drums, painted black, along the back wall, either on the ground or partly buried in the soil.

And if you really want to help heat the frame bed, bury a mixture of fresh manure and straw or wood shavings under the bed's soil . . . and create what's called a hotbed. The decomposing pile will generate heat for your plant's soil. Don't use manure alone for this purpose: It'll cook too hot and too quickly, possibly harming your plants with excess ammonia gas.

HOW TO USE A CLOCHE OR FRAME

If you're new to this art of gently coaxing plants to grow out-of-season, you need to know that such "solar-intensive" gardening is demanding. So start small—just try out one tunnel cloche or cold frame this season—and construct your plant shelter as near to your house as possible.

Since you will be working with a limited amount of sheltered space, do everything you can to utilize it efficiently. Plant in wide beds, not in single rows, and eat all you harvest (including broccoli leaves, carrot tops—in salads—and cut-up greens stems). Just as important, create the best possible soil for your crops. Compost and fertilizing amendments are vital, since most of the commonly grown winter vegetables are heavy feeders and will be growing under somewhat stressful conditions.

Maintaining proper moisture levels is another way of promoting maximum growth and reducing plant stress. You'll probably need to water deeply only once a week in the fall and spring . . . and even less during the coldest months of winter. You certainly don't want to overwater, since that can lead to damping-off and other diseases.

Just as critical as the amount of liquid you provide is when you supply it and what temperature it is. Never water a cold frame or cloche in the evening; that would only make the plants colder during the coming night. If you have no means of heating your liquid, the best time to water is in the morning—then the heat of the day can help warm the water, air, and soil together. (The water will also provide some additional thermal mass to store that day's heat.) Far better is heating the liquid before you give it to the plants. Hot tap water will do fine. Or simply leave plastic gallon jugs, painted black, in your plant shelter. On a good sunny day, those jugs may reach 80 to 85°F by late morning. The water will then be ready to use . . . probably just at the time your frame needs to be opened up for venting, anyway!

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