A Cold Frame is a growing area heated only by the sun coming through the slanted transparent lid or by the warmth from rotting manure (known as a hotbed). The walls of a cold frame are typically made from insulating materials such as brick or wood to help maintain an even temperature. Some cold frames have transparent walls as well as lids. These cold frames maximise the amount of light that reaches the seedlings in latitudes further from the equator, where the angle of the spring sun is low.
Cold frames have a hinged lid that can be propped open in different open positions to allow the gardener to control the temperature in the cold frame. As spring progresses, the sun may over-heat the cold frame, which must be ventilated to prevent the seedlings from wilting. The lid is progressively lifted as the air becomes warmer and must be secure against wind-blow. A sheltered position is desirable and the slope should be towards the sun. In summer the lid should be fully removed.
Cold frames are extensively used for propagation: they are good for cuttings and also for the germination of seedlings.
Cold frame propagating lettuce