Learn how to build a cold frame and enjoy cool-season edibles, such as spinach and lettuce.
A cold frame is a structure built low to the ground and topped with glass, fiberglass, or plastic, to let in sunlight. (If you have pets or young children, avoid using glass).
Cold frames help hold the sun’s warmth overnight, so your plants don’t succumb to frost or freezing temperatures.
Note: Before you begin, learn how to prepare your space for a cold frame.
Begin by measuring and cutting 2″ x 6″ x 8′ wood to three pieces at 24″ and three pieces at 33″. These will be the sides of the cold frame. Cut 1 x 4 x 10 to three pieces at 36″ each and four pieces at 24″.
Use 3″ screws to make base of cold frame. Be sure to attach sides to front and back.
Diagonally cut a 2′ long piece of 2 x 6′ redwood. This will make your wedge on both sides.
Screw wedges to the top sides of the cold frame base using the 3″ screws.
To make the top of the cold frame, layout four of the 24″ 1 x 4 wood pieces and mark the places where you would make “halflap joints”. This is the part where a table saw would come in handy. Now glue the 36″ pieces to the 24″ long for the vertical pieces. This will make a nice flush cover for the cold frame.
Using the plastic screen clips attach all the 8″ x 10″ Lexan pieces underneath so you have a window. Attach hinges to top first and, when placed on the cold frame, screw the hinges to the cold frame base.
Screw on handle and place where your cold frame will get all-day sun. This is usually the south-facing side of your yard.
Tips for using the cold frame:
- Raise the lid on your cold frame when the temperature hits 40 degrees F or above, so the heat doesn’t build up and cook your plants. Close it in the afternoon to trap warmth overnight. Use a stick to prop the lid open for ventilation on warm, sunny days. Cut notches in the stick so you can control how high to raise the lid. If needed, use a shade cloth to lower the temperature.
- Don’t use glass if your area gets snow or ice. The built-up could break the glass.
- Automatic vents aren’t recommended where snow and ice may keep the vent from operating.
- Angle the cold frame so that the back is higher than the front. This helps capture more light and lets rain run off the roof.
- For extra protection, position the cold frame next to a building.
- For additional insulation, dig 6-8″ into the soil and build your cold frame partly below ground. If you’re concerned about flooding, add a layer of gravel underneath.
- When the temperatures plunge to 20 degrees F or below, protect the cold frame by layering old blankets on top or use electrical heating cables.
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