Cold frames protect plants from the wind and also retain heat. Gardeners use cold frames to extend their gardening season—to get a jumpstart in the spring when seeds are sowed or to prolong the season in the fall for a couple of weeks. Cold frames are also used to "harden off" seedlings that were started indoors. It’s now time to start your cold frame/hot bed if you want to get ahead of the growing season.
Frames can be bought constructed from timber and plastic but concrete blocks or bricks can also be used.
You can even construct a bottomless wooden box and set it in the garden or atop other good soil in a sunny location.
Top the box either with glass (perhaps an old storm window) or a frame covered with clear plastic.
Hinge the cover or add a sliding lid so that it may be opened for ventilation on warm days.
If you have high-sided raised beds, you could add a sheet of glass on top to construct a temporary cold frame.
Temporary frames or "cloches" can also be made by leaning old storm windows tent-style over the plants along the length of the garden row.
To protect individual seedlings, cut the bottoms out of plastic milk jugs and place them over individual plants, holding the jugs in place with mounded soil. During sunny days, remove the caps for ventilation.