How to Build a Cold Frame With Blocks

Cold frames allow you to set garden plants out sooner in the spring or you can use the frame to continue growing cool-season plants well into winter. The cold frame consists of a box with a clear cover that opens and closes. Plants sit inside the cold frame or are planted into the soil within the frame. The sun shines through the glass or plastic lid, which is lifted to vent hot air on warmer days. Use concrete blocks to create a permanent cold frame in your garden and take advantage of its season extending ability.

Things You'll Need

• Shovel
• Concrete blocks
• Stakes
• Glass

Instructions

1. Remove the top 8 inches of soil in a 6 by 3 foot area. Choose an area that receives full sun in early spring and winter and is near your home so you can easily access the cold frame during inclement weather.

2. Set the concrete blocks just inside the perimeter of the excavated area, creating the cold frame wall. Place the blocks so the holes in the center of the blocks face upward, if applicable. Set the blocks side by side so they are touching.

3. Lay a second row of blocks on top of the first, so they overlap the seam where two blocks meet in the first row. If you are using blocks that have holes in the center, drive a wood stake through the holes in the corner blocks to help anchor them.

4. Place the removed soil back into the cold frame box. If you are planting directly in the soil, add any desired amendments such as fertilizer or compost.

5. Set a sheet of clear glass or plastic over the top of the cold frame, such as an old window or storm door. Prop the glass open on warm days by placing bricks or blocks of wood between the glass and the cold frame box.

Tips & Warnings

• Tape over any cracks in old sheets of glass and plastic to prevent the warm air inside the cold frame from leaking out.

• Lay blankets or sacks of leaves over the top of the glass on freezing nights to help preserve the warmth in the frame.

• Adjust the size of cold frame to meet your needs or match the size of the glass you are using.

References

• University of Missouri Extension: Building and Using Hotbeds and Coldframes
• Ohio State University: Cold Frame, Hot Bed Construction and Use