A cold frame is an enclosure with a hinged top, used to protect plants from excessive cold or wet. The top is transparent, usually glass or plastic, which admits sunlight and prevents heat from escaping, especially at night.
A cold frame functions as a miniature greenhouse to extend the growing season. They create microclimates that provide higher air and soil temperatures while sheltering young plants from wind.
Cold frame greenhouses allow plants to be started earlier in the spring, and to survive longer into the fall and winter. They are commonly used for growing seedlings that are later transplanted into open ground.
This one is easy to build and stands at a comfortable height. They can also be purchased as kits or ready-made units.