Garden Cold Frames – Build a Cold Frame to Extend Your Garden Season

A cold frame is one of the old standby garden tools. It’s great for extending your garden season, but it’s not just for use in colder climates. It can help you get those seedlings in before the hot weather hits even in the South.

A cold frame is simply a raised bed vegetable garden that has a covering over it. Its primary use is to put seedlings outside before they may be ready to go, especially tender crops that absolutely can’t take a freeze, like tomatoes and peppers. It encourages “hardening off” of seedlings, which gradually acclimates the plants to the temperature swings that nature has in store for it.

While this seems natural for some of the colder states, it’s actually good for use almost anywhere. In the South, the summers are so hot that many crops like many tomatoes don’t have enough of a temperate growing season to do well, so getting an early start may be the only way that some of these can be grown.

A hot bed is similar to a cold frame, but will add some type of heat source (even something as unconventional as a manure pile) to warm the box. But a cold frame just has a transparent cover, it might be a clear polyethylene from a commercially made cover, or one of the all time favorites is a discarded window or screen door with the glass insert. A hot bed actually functions like a small greenhouse.

Location – A cold frame usually has a slope to the top of the frame, and it’s best to have the low side facing south to capture as much of the sun as possible. On the northern side you may want to add a windbreak, or place it on the south side of a building. Even a few bales of hay can keep the cold northern winds out of the box. Just be careful to make sure that the full sun hits the cold frame. *MORE BELOW*

Cold Frame with Greenhouse Cover $69.95 Store: Gardener’s Supply Company Mini Electric Greenhouse $45.95 Store: Gurney’s Seed and Nursery Co. Building & Using Cold Frames: Garden Way Publishing Bulletin A-39 $3.95 Store: Amazon.com Books Cold Frame: Hot House With Heated Mat $31.95 Store: MasterGardening.com Cold Frame: Solar Bell Single $35.00 Store: MasterGardening.com Cold Frame, 3′ x 6′ $49.99 Store: Gardener’s Supply Company Shade Cover for Cold Frame $34.99 Store: Gardener’s Supply Company

You can make your own cold frame from scrap lumber. Since its primary purpose it to act as an insulating container, be sure to take care and make it as tightly sealed as possible. Weatherstripping is a must. If you are using a window or door for the top, you may want to size the box to it to ensure a good fit. If your are using a clear polyethylene for the top, make it a thicker type like 4 to 6 mil to improve the insulation. You amy want to make the sidewalls from 2 inch lumber or thicker to keep the cold at bay.

Commercial cold frames are made from both wood and poly, and have both glass and poly covers. These come in small sizes that are simply for starting seedlings, while others are large enough to cover a full sized bed and the cover is simply removed when the threat of freezing temperatures has gone.

Finally, another use for a cold frame is to help plants overwinter in extreme conditions. Perennial plants can get that extra bit of winter warmth to get them through when covered with a cold frame.