How to Build a Cold Frame With Cement Blocks

Cold frames allow you to extend the growing season for your garden. With a cold frame, you can give seedlings a head start in the spring and protect crops from frost in the fall. You can build a cold frame from scrap materials and still harvest cool season crops such as lettuce and greens when there's snow on the ground. Close the frame on cold days and open it on warmer ones. Some people grow crops year-round in cold frames, while others use them only at the beginning and end of the gardening season.

Things You'll Need

• Shovel
• Cement blocks
• 2-by-4 board
• Level
• Glass window

Instructions

1. Remove the grass and weeds from the spot where you intend to erect your cold frame. Choose a spot that receives full sun most of the day. Use the shovel to skim off the turf, then dig down 6 to 8 inches and loosen the soil.

2. Outline the perimeter of your cold frame with cement blocks. The size of your cold frame will depend on the size of your window. Arrange the blocks to form walls the same length and width as the window.

3. Lay the 2-by-4 across the blocks and set the level on top. If the block walls aren't level, dig out a little of the dirt beneath them with the shovel until the blocks are level.

4. Stack the cement blocks on top of each other, offsetting each row for added stability. Make two to three rows of blocks to form walls 18 to 24 inches high.

5. Plant your plants in the dirt inside the cold frame. You can also set pots inside the cold frame.

6. Lay the window on top of the blocks. This forms the top of your cold frame. The glass window allows sun to warm the plants inside, but the concrete blocks insulate the interior of the frame against the cold. On sunny days, the blocks soak up heat from the sun and radiate it to the plants at night.

7. Lift off the window to tend to the plants.

Tips & Warnings

• You can fasten the cement blocks together with mortar to make a permanent cold frame.

• Avoid setting your cold frame where it will be shaded by buildings or trees.

References

• Savvy Gardener: Cold Frames and Hot Beds
• University of Missouri: Building and Using Cold Frames

Resources

• Virginia Cooperative Extension: Season Extenders