A cold frame is a protective covering and passive solar-energy collector for growing plants when cooler temperatures outdoors can adversely affect plants. A cold frame protects the plants from sudden temperature changes, chilling winds and frozen precipitation.
The basic structure of a cold frame is four walls and a lid. The lid is made with a clear material that allows sunlight in. The walls can be solid wood or a clear material to allow more sunlight into the cold frame. Portable cold frames are placed over plants either in an outdoor garden or pots; and therefore do not have a floor.
A modern evolution of the cold frame is the switch from an old window sash with glass panes for the lid to polycarbonate panels. Clear polycarbonate panels have the same light transmission properties as glass and are much lighter in weight. The use of Do-It-Yourself friendly polycarbonate panels also enables variety in the length and width of cold frames. The cold frame shown here was made with cedar—a naturally rot-resistant wood—and TUFTEX PolyCarb Clear panels.
Home gardeners appreciate the versatility of a cold frame for starting seeds early, hardening off seedlings, extending the growing season for cool-weather crops, and overwintering dormant plants. The cold frame also protects plants from animals and insects.
For starting seeds early, a cold frame is similar to a greenhouse. Warmth from sunlight is trapped inside the cold frame to provide a suitable environment for seeds to grow.
For hardening off seedlings, a cold frame provides a controlled transitional outdoor environment for plants that sprouted indoors and are destined for an outdoor garden. Some gardeners use a cold frame for starting the seeds and hardening off the seedlings in the same soil, which eliminates transplanting shock for the plants.
Low-growing, cool-weather crops—such as beets, broccoli, brussels sprouts, cabbage, collards, carrots, cauliflower, lettuce, mustard greens, onions, radishes and spinach—grow well in the protected environment of a cold frame and provide nutrient-rich food after the normal season has ended.
For overwintering plants, a cold frame provides the right conditions for a gentle dormancy, and helps the plants to resume growth in the spring.
For more inspiration on cold frame designs, we offer these examples on https://www.pinterest.com/explore/cold-frame/
For more information on gardening with cold frames, we recommend http://www.finegardening.com/4-ways-use-cold-frame#ixzz4uqwiQkVZ.