Using Cold Frames in the Organic Garden

It is the dream of many organic gardeners to have a large greenhouse to grow tropical plants and start seeds all year. However, many gardeners have neither the space nor the money to install a full sized greenhouse. A cold frame can act like a mini greenhouse, allowing the gardener to extend the growing season well beyond the first frost.

What is a Cold Frame?

In its simplest form, a cold frame is a box, usually constructed out of wood, with a clear lid made out of glass, plastic, or fiberglass. A cold frame is for gardeners who are ready to move beyond cloches and floating row covers, but aren’t quite ready to invest in a greenhouse. A cold frame can be mobile, or one can dedicate a permanent space in the garden for this structure.

Buying a Cold Frame

Gardeners can buy a range of cold frames, from a basic model made of a steel frame covered with reinforced vinyl, to a deluxe model fitted with double wall polycarbonate panels. Gardeners should consider the growing climate, and how long they wish to extend the season, when choosing cold frame models.

Accessories can help organic gardeners get the most out of their cold frames. A soil heating cable turns the cold frame into a four-season garden aid. Automatic vent controls prevent tender seedlings from being scorched on unseasonably warm days. Greenhouse bubble insulation helps to trap and retain warm air in cold climates.

Building a Cold Frame

Constructing a cold frame allows gardeners to customize their frame, and to incorporate recycled materials into the construction. If a gardener has an old window, he can simply construct a wooden box that fits the size of the window. Gardeners who aren’t carpenters can erect a temporary cold frame by stacking bricks or concrete blocks to form a base. Creating a slanted lid and orienting the cold frame so that it faces south makes the most of the wan winter sun.

Seed Starting in a Cold Frame

Gardeners can start seeds under the cold frame in the ground or in flats. Some seeds are fussy about germination temperatures, so a thermometer is helpful to determine the right time to start seeds. Gardeners can line the bottom of the cold frame with black cloth or plastic to capture the heat of the day and speed up germination of warm weather annuals and vegetables.

Cold Weather Vegetable Gardening

If the cold frame has a generous height allowance, at least 24 inches, the gardener can use it to grow cool weather vegetables like spinach, lettuce, radishes, or carrots. An added bonus is that the cold frame acts as a barrier, keeping out hungry insect pests and rabbits. The cold frame may prove to be too effective, in that it raises temperatures too much for cool weather vegetables. A piece of shade cloth cut to the cold frame’s dimensions can provide heat relief if the salad greens are bolting early.