From Longman Dictionary of Contemporary Englishcold frameˈcold frame noun [countable] British English a box-like structure with sides and a top made of glass or clear plastic, used for keeping young plants warm as they start to grow
Examples from the Corpus
cold frame• In August, sow early carrots in a cold frame or greenhouse and keep covered during winter for pulling as needed.• Stand boxes of cuttings in a cold frame or under greenhouse staging and keep slightly moist.• Water well. 4 Label the pot and put on a cool bench or in a cold frame.• Before planting outside, they will require a short hardening-off period in a cold frame or cool greenhouse.• Because polyanthus are more difficult to germinate, start them off in seed trays or pots in a greenhouse or cold frame.• A mini greenhouse or cold frame would be a good alternative in small gardens.• Cyclamen may also be raised from seed sown now in pots and pans and put outside in a shaded cold frame.• Keep the plants cool, putting them in a shaded cold frame. 