A SEED-STARTING SOLAR COLD FRAME

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Plant your cold-sensitive vegetables before the last spring frost with . . .

A cold frame is one of the best ways for an aspiring gardener (especially one whose bankroll won't support the purchase or the construction of a full-sized greenhouse) to get a head start on a summer vegetable plot. In most parts of the country, one of the mini-hothouses will help you beat the final spring frost by three to four weeks . . . and it can even extend the growing season enough to let you get in an extra succession planting!

Cold frames aid growing plants in two ways. First, the devices admit sunlight to enable seeds to sprout into up-and-coming edibles. And, in much the same fashion as do solar collectors, they convert solar energy to heat ...in this case to maintain air and soil temperatures which are conducive to growing. Consequently, the two major concerns when designing a cold frame are to let the sun's rays in , and to retain heat.

In keeping with state-of-the-art energy efficiency, we have designed a passively solar, earth-sheltered, and well-insulated cold frame. The box is built from a sheet of inch-thick, toil-backed foam insulation board. Using the technique developed while constructing MOTHER's Heat Grabber (the article ran in No. 47 . . . see page 148 of this magazine for back issue ordering information) and used frequently in subsequent solar projects, we trimmed out 7" corners from a 39" X 61-1/4" section of the insulation, and carved 90° grooves in the foam so that the sides and ends could be folded up without our having to cut the exterior foil. (See the small illustration for details. Note that — in order to achieve the proper angle — the slicing tool must be drawn first along one side of the half-round-molding guide, then reversed to cut along the other side.)

Once the insulation board was shaped to the dimensions shown in the large drawing, we further insured a good seal by lining the joints — inside and out — with metal tape.

Two triangular frames built from 2 X 2 lumber hold up the corrugated fiberglass lid, and the 18" X 18" X 25" (outside dimensions) sides describe an isosceles triangle. Once the pieces have been mitered and screwed together, tack on 18"-long strips of ripple board, and connect the two frames by butting 44" lengths of 1 X 2 between them.

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