How to Make an Outdoor Cold Frame

Cold frames can exend the length of your growing season.

For those without the space or the money for a large greenhouse, a cold frame is a great way to extend the growing season. Cold frames are the essence of simplicity: a few old windows are supported on a frame with the young plants underneath them, thus keeping off the frost at night and trapping the heat of the sun during the day, making it summer inside the cold frame, even when it's early spring or late fall outside. These instructions can be modified to fit any old windows you may have.

Things You'll Need

• 3 old windows, 20 by 30 inches
• 3 pieces of plywood, 3/4 inch thick, 4 inches wide, 20 inches long
• 3 pieces of plywood, 3/4 inch thick, 12 inches wide, 20 inches long
• 6 pieces of plywood, 27 1/2 inches long, 4 inches wide on one end and 12 inches wide on the other end
• 6 hinges
• 30 screws, 2 inches long
• Drill or screwdriver
• 3 latches

Instructions

Build the Frames

1. Place one of the 4 by 20 inch pieces of plywood against the 4 inch wide end of one of the pieces that is 4 inches wide on one end and 12 inches wide on the other. Screw them together using two screws.

2. Screw another one of the pieces 4 inches wide on one end and 12 inches wide on the other onto the other end of the 4 inch wide piece.

3. Screw one of the 12 inch wide pieces of plywood onto the 12 inch wide ends of the two side pieces. You now have a four sided, open bottomed and open topped box, 12 inches tall on one end and 4 inches tall on the other.

4. Do the same with the other 8 pieces of plywood so you have three identical boxes.

5. Increase the strength of the boxes by screwing small triangular scraps of plywood onto the bottom corners.

Attach the windows

1. Screw two of the hinges onto one of the 20 inch sides of one of the old windows.

2. Lay the window on top of one of the boxes so the hinges hang down along the vertical face of the 12 inch high side. Screw the hinges onto the side. The window should now be sitting on top of the box, and secured by hinges on one end.

3. Plane, cut, or otherwise modify the window and/or the box as needed to create a secure fit between window and box. You should be able to lift the window easily and then close it again so that it meets with the top edge of the box at all points.

4. Attach a latch at the bottom of the window for added security and to protect plants from wind and predators.

5. Put a 26 inch long stick on the ground inside each of the cold frames. Use this stick to prop up the window when you are working inside of the cold frame.

References

• "The caterpillar cold frame: How to build a cheap, simple structure that extends your gardening season", Steve Marlens, 1980
• Groovy Green: How to Build a Cold Frame
• 5Min: How to Build a Cold Frame