Cold Frame - A Simple Greenhouse

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A cold frame is essentially a ground level, unheated greenhouse. It is usually a glass or plastic covered box which is mostly used to harden off seedlings before planting them in the garden. It differs from a cloche in that a cold frame is usually more permanent, whereas a cloche is portable and temporary.

Plants in a cold frame are usually in pots or bedding packs. A cloche usually covers plants in their permanent locations in the garden. The seedlings are usually started elsewhere, in a greenhouse, germination chamber, or hotbed. Then they are transplanted to the cold frame to allow them to acclimate them to the cooler outdoor temperatures without subjecting them immediately to the rigors of the ever changing temperatures and wind of the outdoors.

The cold frame can be protected by a blanket or similar cover on nights when the temperatures dip lower than the plants inside can tolerate. Since there is no heat, and the sides and cover usually provide minimal insulation against protection against the extreme temperature swings of early spring is important.

A cold frame can be constructed using wooden boards, using an old window sash or storm window for a cover. A cover can also be constructed using a window screen onto which clear plastic has been stapled. A prop should be provided so the lid can be propped up during the sunny days, to prevent the inside from becoming overheated.

The cold frame can also be used to over winter perennial and shrubs in small pots. The cold frame will protect the small plants from the drying winter winds and help moderate the cold temperatures. Any snow cover on top of the cold frame can also help protect the small plants.

A cold frame is an ideal structure to protect small seedlings in the spring before they are ready to set in the garden. It will help harden off theses small plants. It may also be used to over winter small perennials and shrubs in pots.

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