How to Build Cold Frames
Simple project to protect tender plants in winter
Used to protect tender plants or rooted cuttings during the colder months, a cold frame is simply a box with a transparent lid or cover. It acts as a passive solar energy collector and reservoir.
During the day, the sun’s rays heat the air and soil in the frame; at night, the heat absorbed by the soil radiates out, keeping the plants warm.
A cold frame is useful at other times of year as well. In spring, it provides an ideal environment for hardening off annual flower and vegetable seedlings started indoors. Seeds of many plants can be sown directly in the frame and grown there until it’s time to transplant them to the garden. In summer, you can replace the cover with shade cloth or lath, creating a nursery for cuttings.
Set up your cold frame in a site protected from harsh winds by trees, shrubs, a fence, or a wall. To ensure that the frame will receive as much sunlight as possible, orient it to face south or southwest.
Sinking the frame 8 to 10 inches into the ground increases heat retention significantly. Make sure the location has good drainage, since you don’t want water to collect around the frame after every rain.