Here are tips on how to make cold frames for the garden. When those first frosts hit, you’ll want to protect those precious plants! Try building your first cold frame!
What is a Cold Frame?
Cold frames are usually bottomless boxes that are set over plants in the garden to protect them in adverse weather. They are usually built low to the ground and have a transparent roof with a hinge.
Why Use a Cold Frame?
Cold frames protect plans from the wind and also retain heat. Gardeners use cold frames to extend their gardening season—both in the autumn to protect plants for a few more weeks and also to get a jumpstart in the spring when seeds are sowed. Cold frames are also used to “harden off” seedlings that were started indoors.
- Try sowing seeds of crops such as radish, lettuce, endive, and scallions directly in the frame for an early or late harvest.
- You can even raise them there all summer as long as the cover is removed when warm weather arrives.
- Consider growing winter lettuces of other salad leaves.
How to Make a Cold Frame
Frames can be bought constructed from timber and plastic but concrete blocks or bricks can also be used. You can even construct a bottomless wooden box and set it in the garden or atop other good soil in a sunny location. Most gardeners use wood to build the frame, since it’s readily available and is easy to cut to the required size using hand tools. If you’re lucky enough to find scraps of hardwood then use this, as it will last longer than softwood. Avoid old wood that’s been treated with creosote or similar non-earth-friendly products, especially if you’ll be positioning the cold frame directly on the soil. The wood can always be painted with a non-toxic paint if you’re worried about it looking scruffy.
Top the box either with glass (perhaps an old storm window) or a frame covered with clear plastic.This should be made of glass or tough plastic. Old windows and shower doors are classic subjects for this project. Hinge the cover or add a sliding lid so that it may be opened for ventilation on warm days.
If you have high-sided raised beds, you could add a sheet of glass on top to construct a temporary cold frame.
Temporary frames or “cloches” can also be made by leaning old storm windows tent-style over the plants along the length of the garden row.
For those of us with limited time and/or DIY skills, try cutting the bottoms out of plastic milk jugs and place them over individual plants, holding the jugs in place with mounded soil. During sunny days, remove the caps for ventilation.
How to Make a Hot Bed
A hot bed is a cold frame that is heated. The method of using horse manure or compost works well and is more economical than electric heating cables.
- For a nonelectric hot bed, excavate 18 to 24 inches under the frame and add fresh manure or compost.
- Turn and moisten this material every couple of days for a week until it settles, then cover it with 6 inches of soil.
- As the manure or compost decomposes, it will generate enough heat to protect against early or late frosts.