Extending The Season

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There are other simple ways to make tunnel cloches. You can make your hoops of spring steel poked into the ground. Lay your plastic over those, then run a second hoop or string right next to each of the supporting ones to hold the plastic in place (see Fig. 3). Or you can use reinforcing wire mesh arched over the bed (cut the material so both sides have lots of wire ends to poke into the ground) and cover that with plastic (Fig. 4).

THE COLD FRAME

Tunnel cloches are definitely the "hot" plant protector at the Eco-Village these days—we're using them more and more. But we're far from abandoning our other small-scale season extender: the cold frame.

A cold frame, essentially, is a bottomless box (usually of wood) that faces south, is higher in the back (the north side), and is covered with glass or plastic. Cold frames are durable, attractive, easy to use, and—because of their increased insulation—probably better at protecting plants from extreme cold than the all-plastic cloches. On the other hand, they do cost more to construct than tunnel cloches: The materials for the 4' X 6' model shown in Fig. 5 cost around $150, not counting the glazing. And although you build such a miniature greenhouse from the bottom up, you should design it from the top down . . . in other words, it's easier to get your glass (or other glazing) first and build the frame to fit it. If you can scrounge up some usable windows or glass door panels, you'll have trimmed a considerable expense.

You'll want to build your cold frame so the top slants southward, but don't worry about trying to get the "best" sun-catching angle; that's usually not critical. Do be sure to paint the interior white to help diffuse the admitted light, though.

Unless you'd prefer to have a portable cold frame, you'll want to lay some type of foundation. You can use concrete block, rot-resistant wood (such as locust, cedar, or cypress), or lumber painted with a latex acrylic paint or a homemade preservative of copper naphthenate or linseed oil. (Never use creosote or pentachlorophenol on a cold frame.) Lay this below frost level and insulate it with closed-cell foam board insulation. You might also be wise to place gravel under and around your frame's foundation to improve its drainage and to help protect the wood.

For glazing, use glass if you scrounged up windows . . . 6-mil polyethylene if you want to skimp (and have a very temporary covering) . . . or a fancy fiberglass-reinforced plastic (FRP) if you want something durable (and pricey). Since your biggest heat loss will be through the top of the cold frame, you'd do well to double-glaze the top. One of the most practical and cost-effective ways to do that is to use glass on the top and plastic underneath. The glass will help filter ultraviolet rays, which deteriorate plastic. And if the glass should ever break, the plastic may help catch the pieces!

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