Mother's Deluxe Four-season Cold Frame

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Another great thing about MOTHER'S cold frame is that it offers protected venting situations. I've seen enough sudden spring hail—and thunderstorms that I don't feel com fortable leaving a cold frame open to the elements—even if it's the middle of the day and the sun's blazing down. With this model, air can flow through from the sides while the "roof" still protects from above. (If the wind's too strong from one side, we'll cover that end with a window sash or piece of plywood.) That also keeps me from having to keep the glass cover completely shut on overcast and wet days—a situation that just invites disease.

Construction

No matter how well designed a cold frame is, it won't do much good in a bad site. Your first priority should be to choose a spot with good sunlight that faces close to due south. Proximity to the house comes second, to make the box easier to tend. (Be sure, though, that snow or ice can't slide off your house roof onto your cold frame.) And if you have a drainage problem as I did with my first plant box, underlay yours with gravel and plastic drainpipe.

The accompanying illustrations can do most of the talking about how to build MOTHER'S cold frame. I'll just give some general advice and cover a few specifics.

1) glass cover down 2) glass and reflecting covers slightly open, 3) glass and reflecting covers up high, 4) both coversoff 5) both covers down.

Cold frames are by their very nature subject to severe water stress. In my experience, no paint job will protect them for long. So I built this model out of rot-resistant west coast cedar. I'd recommend it or some other naturally weather-tough wood. (I wouldn't use pressure-treated lumber myself; I'd be afraid it might damage or contaminate the plants.)

Since the box's main job is to protect crops from cold, I made the walls out of extruded polystyrene board (don't use beadboard; it soaks up water), to provide insulation, and caulked every joint before nailing, to reduce air infiltration. Also, to help the structure stay snugly together, I liberally applied construction adhesive during assembly, along with using ordinary nail-and-screw fasteners.

I designed the cold frame around the glazing — in this case, a standard, single-paned, 76 " X 34" sliding-glass-door replacement panel. I like glass: It's durable and attractive. And door panels are made of tempered glass and are readily available.

I did have to make a frame for the glass (probably the most exacting step of the entire project) by cutting 3/16"-wide grooves 1/8" deep in one side of some 2 X 2 stock. After gluing and screwing those on, I put 36" pieces of 1 X 4 on the frame sides to add extra strength and to serve as handles.

The box was built to fit the glazing. It has a 2 X 6 frame (with 1 X 4 legs). The four 16 "-wide polystyrene walls can be cut out of one 8' sheet of the insulation board. They're lined on the inside with 1/8"-thick sheet fiberglass (it's sold as mobile-home underpinning) to protect them from periodic digging. Cut this inside liner 1/2" wider than the polystyrene so it can lap over the frame for a tight seal. Note: Put the liner on the long insulation pieces before you push in the side ones. That way you can fit the walls and liner together snugly at the corners.

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