A Cold Frame, or a Hot Box, Can Extend the Gardening Season
Cook, Adrienne, St Louis Post-Dispatch (MO)
In Europe they are called hot boxes; in America, we call them cold frames. Whatever their name, they are invaluable devices for flower and vegetable gardeners alike and are surprisingly simple to make.
A cold frame is a large, bottomless box topped with a glass or glazed lid angled to intensify the light and warmth from the sun.
By trapping the sun's rays, the frame raises both daytime and nighttime temperatures, allowing cool-season crops to grow through the winter, forcing spring bulbs and giving annuals and early season crops a jump in early spring.
Unlike greenhouses, cold frames are not heated and are not for varieties that cannot tolerate freezing temperatures. Despite the frame's ability to attract and trap heat, it is not impervious to prolonged cold.
The value of a cold frame is in extending the garden season at both ends, and with it all the pleasures and duties that go with plant cultivation. In the spring, the gardener can start varieties a month or more early - among them celery, broccoli, lettuce, peas, beets, cabbage and parsley. In the fall, the cold frame can double as a winter garden, allowing the cultivation of small amounts of cold-hardy annuals, such as lettuce, spinach, parsley, cilantro and carrots.
The cold frame also is handy for gardeners who want to force spring bulbs - the relative warmth inside causes bulbs to break dormancy early so they will bloom in midwinter indoors. Most spring bulbs need a period of chilling in order to bloom. Storing them in a cold frame starting now will accomplish that.
In the spring, the cold frame also will prove its worth with warm-weather annuals: It makes an ideal transition place for tender seedlings that need to be hardened off before setting in the garden proper.
Even in the summer the cold frame becomes a great holding bed for seedlings.
Fall is the best time of the year to set up a cold frame. The leaves have fallen from the trees and the gardener can site the box accurately - facing south in alignment with the low, southerly winter sun. …