How to Build a Cold Frame

Cold frames are a great way to keep plant starts warm while it's still too cold to plant directly in the ground and to harden off plants prior to planting. They allow gardeners in cooler climes to start seeds in late winter and get a jump on planting once spring comes.

But if you look up these season extenders online, they can cost you anywhere from $50 to $200. Why spend this kind of money on a cold frame when you can build your own for much less? Finding supplies was an easy task with my local Re-Use It Center in McPherson, Kansas, which sells a wide range of reusable items for a low cost - from wood and windows to paint, screws and household appliances. In one trip I collected two large pieces of 3/4" plywood, a can of exterior latex paint, a couple of windows and screens, hinges and handles, all for just under $30. Take a look around your own town and see what it has to offer. If you don't have a re-use center, ask around to see if anyone has scraps they're looking to get rid of.

To build your cold frame, you will need:

• 3/4" plywood or similar, with dimensions large enough to accommodate the size of your cold frame(s)
• Exterior paint to seal the wood and keep it from rotting
• Handles for two sides
• A window or some sort of clear glass or plastic pane to allow the sun through
• Screws, and bolts with washers
• Power drill
• Power saw
• Hinges for the window frame

To build the cold frame:

• Determine the dimensions of the cold frame. Do this by measuring your window, but keep in mind that with the slope of the frame, the length from front to back will be slightly shorter than the width of the frame.

• A one to two inch slope per foot front to back is recommended to allow the right amount of sunlight into the cold frame.

• Cut your front, back and side pieces of wood, in addition to some support slats for each of the four corners.

• Paint each piece of wood prior to putting the cold frame together and again once you've constructed it.

• Use a power drill to construct the cold frame.

• Place the window frame on top of the cold frame to be sure it fits properly and then make marks for your hinges. 

• Drill the hinges into the window frame and then into the back of the cold frame.

• Using the power drill, attach the handles to each side of the cold frame for ease of transport.

• Set the finished cold frame(s) outside facing south and you're ready to go! Consider placing strawbales around the sides of the frame to give it extra warmth. You may also want to add some manure inside the cold frame to generate warmth as well.