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Cold Frames; How and Why

Cold Frames are basically wooden boxes with no bottom and a glass top that you place on top of crops to keep them warm. In this article, I’ll give a few tips on how to get cheap material, maximize the benefits through design, and explain why you should use cold frames if you live in a zone that has harsh winters.

The windows are the part of the cold frame that can make construction costly. If you were to purchase them new the cost would likely outweigh the potential gains. You can however, get lucky if you keep your eye out at stores like Home Depot for windows that have been damaged and are being sold cheap. If you or someone you know is remodeling their home you can get windows for free there, if you drive past a house being remodeled you can stop and ask permission to check the dumpster. If you have a habitat for humanity restore shop in your area you might find cheap windows there as well.
The frame should be made to fit the window so that the window can simply sit on top of it, hinged if possible so that you can easily open it to harvest and to check on your crops.
Since a cold frame works by magnifying the sun’s light with the glass to increase the heat inside the box, you want to maximize the amount of sunlight that gets inside. To do this want to have your glass tilt down on the side that will be toward the sun. For this reason, you will want to have the back side a few inches higher. If you use a 2×8” on the back and a 2×6” on the front this should be enough of a tilt, if you need more after you have constructed it you can always mound some earth up on the back side to raise it a little.
With a cold frame, you will not only be able to extend your growing season for your warm weather crops, but you can also grow perineal crops all through the winter in some cases, and you will be able to begin growing and harvesting much earlier in the spring.
Remember that cold frames are “solar powered” and will not work in areas that are shaded during the winter.

Gardening doesn’t have to be a seasonal activity if you have the right equipment. As you add layers of protection to your garden you add time to your growing season and volume to your harvests.

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