Mich. The outdoor gardening season is still weeks away, but the sweet, spring-green tips of lettuce and spinach already are poking through the soil on John Biernbaum's farm near East Lansing. The plants are growing in a cold frame that Biernbaum built from old shower doors and scrap wood. Gardeners get pretty creative when it comes to scrounging up the necessary components for cold frames, which are bottomless boxes or frames placed over the soil.
Sunlight goes through a clear or translucent cover, warming the soil below.
The cover and sides protect the plants from wind and the wild temperature and moisture swings so common in late winter. Cold-tolerant plants like spinach, carrots, certain salad greens and parsley can survive inside, ready to harvest earlier or later in the season than possible in an open garden. And because sunlight starts intensifying a critical factor for plant growth in February and March, the growing season gets off to an early start inside a cold frame. You can even pick spinach when there is still snow on the ground. In fact, dozens of vegetables can survive outdoors with winter protection like cold frames.