coldframe

A cold frame is a transparent-topped outdoor enclosure used to protect plants from cold, wind, and frost while extending the growing season. It typically consists of a shallow or raised frame made of wood, brick, or plastic, with a hinged or removable cover of glass or clear plastic. The frame is usually placed in a sunny location, often against a wall or elevated to improve drainage and heat buildup. Inside, the interior acts as a small solar greenhouse, warming during the day and venting to prevent overheating.

Uses include starting seedlings earlier in spring, hardening off transplants, protecting overwintering perennials, and extending the season for crops in autumn. Construction can vary from simple wooden boxes with a lid to more elaborate raised beds with shelving and soil beds. Covers may be glass, polycarbonate, or polyethylene, and some designs include vents at the top or sides for air exchange.

Operation involves managing temperature and moisture. On sunny days the lid is vented or propped open to avoid overheating; on cold nights it may be closed to conserve heat. Watering is needed as the soil can dry out quickly, and occasional cleaning helps prevent disease buildup. Cold frames are generally used in temperate climates and can be temporary or semi-permanent installations.

Advantages include low cost, energy efficiency, and the ability to extend the growing season without active heating. Limitations are limited temperature and humidity control, potential overheating in bright sun, and susceptibility to drying and pests. Variants include freestanding frames, integrated bed designs, and wall-mounted units.