Cold Frames 

Usually permanent structures of brick with framed glass "lights," cold frames are useful for hardening off young plants and extending the productive season of crops such as salads and zucchini. Constructed in a sheltered, sunny spot, they are a good alternative to a greenhouse in a small garden, with the angled lights allowing water to run off and the maximum amount of light to reach the plants. A frame with a hard base is suited to acclimatizing pot-grown plants to outdoor temperatures, while a bed of improved soil allows crops to be grown in the frame. Prop the lights open during the day to provide ventilation, and keep plants inside well watered.