Want to get a head start on spring by starting your own plants from seed but don’t own a greenhouse? The solution is a cold frame: a bottomless box with a lid which admits light.
The recommended workable size of a cold frame is three by six feet, 15 inches high in back and 9 inches high in front. The slope of the lid will capture maximum sunlight and allow for rain runoff. The sides can be made out of wood, brick or foam insulating builders board. The top can be made out of a window sash, a storm window, or polyethylene film in a simple frame. It should be hinged in back to allow for venting.
The best site is a southern exposure that is protected, receives plenty of sunlight and has good drainage. It is helpful to have a water source close by.
Temperature and moisture are the two most important management factors. The temperature should be kept around 75 degrees and can be monitored by placing a thermometer inside. Heat can quickly rise to over 100 degrees on a sunny day but can be easily managed by raising the lid for ventilation. Water the seed flats when the soil begins to dry.
Sounds like a lot of work? It really is not. Cold frames have been used for centuries, and using them to get an early start on the growing season can be very rewarding.
Sue Adee, Smith County Master Gardener
Texas A&M AgriLife Extension Service