In the Garden:
This purchased cold frame combines a wood frame with double-walled polycarbamate sides. A new top is on this spring's "to do" list.
Shelter from the Storm
Among the items to add to the list of "everything that's old is new again" are the various types of season-extending shelters for plants. These include cold frames, cloches, water-filled plastic cylinders, tunnels, and garden fabric. In gardening manuals from a hundred years ago, cold frames and cloches were gardening staples for starting seedlings and cool-season crops, growing vegetables longer into the fall, overwintering tender plants, and propagating woody plants. Twenty years ago, you hardly ever saw any of these. Open a garden supply catalog now or do a Web search, and you're confronted with dozens of choices.
Homemade Cold Frames
Cold frames are basically mini-greenhouses that sit low to the ground. For most of their history, they were most often made with wood walls and a glass top. With modern materials, we're no longer limited to wood and glass, although these are still among the cheapest and easiest materials to use. Packrats and scroungers will have the materials already on hand -- scrap lumber and a discarded window sash. Others can head to their local lumber supply store. If growing food crops, don't use pressure-treated wood. "Average" dimensions are 3 feet wide, 4 to 6 feet long, 12 inches high in the front, 18 inches high in the back, with sloping sides to better catch the sunlight. The best location for a cold frame is somewhere sheltered from the wind but with a southern exposure.
By hinging the window, it can be easily propped open on warm days. You can also purchase thermostatically controlled arms that open the top when the temperature inside reaches a specified level. Because of the heat buildup in a cold frame, plants will dry out more quickly then they do in the garden, so it's important to keep an eye on soil moisture. By adding a heating cable to the box, you have what's known as a hot bed.
Purchased Cold Frames
Purchased cold frames often have metal or PVC frames with plastic or double-walled polycarbonate walls or cover. They are available in a wide range of shapes and sizes, but most have a rounded or A-frame top. Taller models, sometimes up to 3 feet in height, allow you to grow larger plants.
Many purchased cold frames are light in weight, so they must be firmly anchored to keep them from blowing away in a strong March gale. The advantage to being lightweight is that they can be readily moved to various parts of the garden as needed.
A variation on cold frames is to put plastic or garden fabric (a white, semi-opaque material that resembles the interfacing used in clothing) on hoops over raised beds or wide garden rows. Hoop supports can be purchased or made with flexible PVC pipe put over 18-inch lengths of rebar sunk in the ground. These tunnels can be as long as reasonable, but are usually 2 to 4 feet wide. The ends are opened and closed as needed for air circulation and to maintain desired temperature. Be sure to anchor the sides with earth staples or rocks.
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