Cold Frames.  A cold frame is a transparent-roofed enclosure, built low to the ground, used to protect plants from cold weather. The transparent top admits sunlight and prevents heat escape via convection that would otherwise occur, particularly at night. Essentially, a cold frame functions as a miniature greenhouse season extension device. 

Cold frames create microclimates that provide several degrees of air and soil temperature insulation, and shelter from wind. In cold-winter regions, these characteristics allow plants to be started earlier in the spring, and to survive longer into the fall and winter. They are most often used for growing seedlings that are later transplanted into open ground, and can also be a permanent home to cold-hardy vegetables grown for autumn and winter harvest. 

Cold frame construction is a common home project, although kits and commercial systems are available. A traditional plan makes use of old glass windows: a wooden frame is built, about one to two feet tall, and the window placed on top. The roof is often sloped towards the winter sun to capture more light, and to improve runoff of water, and hinged for easy access. Clear plastic, rigid or sheeting, can be used in place of glass. 

(Thanks, Wikipedia.)

Ruby Garden has about ten cold frames available for plotholders to use, and we also are happy to show you how to make your own.  Please contact us if you are interested in having a cold frame.  For those interested in making your own, here are some good plans.