Cold Frames: A Way to Extend Your Growing Season

By Pat Dickey, Fairfax Master Gardener

old windows and cedar frame

If you are looking for a way to begin your vegetable gardening earlier and to extend the growing season by several weeks, why not use a cold frame? You will be able to grow leafy greens and other crops that are adaptable to colder weather in early spring, late fall, or in winter if the temperatures aren’t too frigid. You will also be able to cover existing plants in the fall prior to frost to extend their harvest. The cold frame will also be a place to harden off your seedlings before planting them into your garden. It provides a way to transition your seedlings to the outdoors or to keep your seedlings protected until the weather is warm enough for them.

A cold frame is a bottomless box with a clear or translucent, removable top. Woods such as cedar or cypress are best for the base of the frame because they won’t decay. The size of your cold frame depends on how much space you have and how many seeds or seedlings you want to plant inside. Try to make your frame about 3 to 4 feet wide so that you can easily reach across it to tend to your plants. Remember to water what is growing inside the cold frame, because it will not receive any natural rainfall.

aluminum & lucite cold frame

commercial cold frame with lucite and aluminum frame

Polyethylene or a Lucite sheet of plastic are most suitable to use for the top of the cold frame. Many gardeners also use windows as the top. Older windows should be checked for possible lead-based paint. County community gardening also prohibits the use of glass inside the p