A cold frame is used to grow winter seedlings and crops effectively by protecting the plants from the excessive cold. Consisting of an enclosure built low to the ground and having a transparent-roof, a cold frame functions as a miniature greenhouse and substantially increases the growing season. The solar energy stored during the day provides plant-protecting heat in the structure allowing the plants to keep growing.
The best-built construction does no good in a wrong spot. When constructing a cold frame choose a location that faces south with plenty of sunlight. To capture reflected heat, build the structure against a building or wall. The heat and light will reflect off the surface into the frame. Plants will not survive in wet conditions, so good drainage is another site requirement. Water should not enclose the structure. Build the open-bottomed frame over good soil or a raised bed for the growing medium. Provide plants with a top layer of six inches or more of garden soil.
Frost-tolerant leafy greens crops, such as kale, mustard greens, romaine lettuce, spinach, and chard, are grown easily in cold frames. Other vegetables that grow successfully are carrots, green onions, and radishes. Consider the plant’s life cycle when making a selection. Vegetables that germinate in fall, grow during late fall and winter, and then go to seed in spring are good choices.
A “poor man’s greenhouse” gives a big advantage to winter gardening by providing yields into the spring and a head-start on the next season.