A few years ago, while driving with my family through the countryside of Bulgaria, I noticed how strikingly similar the landscape was to that of central Virginia. I also noticed that nearly every home had a garden plot, a grape arbor, and a cold frame of some sort. It made me realize how ancient and universal the practice of using cold frames is.
A cold frame is a simple structure that utilizes solar energy and insulation to create a microclimate within your garden. For those of you who have harvested and eaten a salad of fresh greens in February or have flowers blooming well past frost, you know the attraction of using cold frames. You also know how easy they are to make and use. Although we have a greenhouse on our farm, space is always limited, so we rely heavily, especially in spring and fall, on our cold frames to overwinter plants, extend the growing season, start seeds, and harden off plants.
For whatever purpose you want to use a cold frame, you need to keep in mind a few basic factors. First, some plants fare better in cold frames than others, with low-growing, cool-season plants being the best suited. Second, the type of cold frame you use dictates how much protection you can offer your plants. In all cases, the main conditions you need to monitor and control are temperature, sunlight, moisture, and wind exposure.