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How to Build A Cold Frame

February 16th, 2013 by Trisha

Cold frames are great for all sorts of garden related things… Storing plants you didn’t get a chance plant the previous year. Extending your growing season for cold weather veggies, and hardening off seedlings you started indoors.

Cold frames are so easy to build. Sure you could buy a cold frame kit, but there’s not much to building one yourself. Any scrap wood, any old garbage picked window, even a little plastic and you’re good to go. Some key things to think through when you’re considering how to build a cold frame.

Location.
If you have a south facing location to put your cold frame, preferably close to the house, this will provide the most heat. Size and shape? Thats totally up to you and your location.

Solar Angle
As far as the angle to set the window, the general rule of thumb for winter is your latitute plus 15 degrees for the optimal solar angle.

Air Flow
When its COLD, you want your cold frame to be as air tight as you can get it. That means filling any gaps between the wood or windows. ALSO, it gets super hot in a cold frame when the sun is blazing, even when its not hot outside. It smart to attach your windows with hinges and devise a prop to hold the windows open slightly for ventilation. It’s also smart to invest in a cheap thermometer to monitor your temps.

Here is our south facing cold frame.
how to build a cold frame
Size and shape were 100% determined by the location, the wood and the salvaged windows we had laying around. It could use some soap and water, but overall it blends nicely. I would like it to be a little taller, but we used the materials we had here… temperature reading in mid February was 50 degrees, on a 30 degree day. Not bad.

Another smaller (prettier) cold frame at a better solar angle. Wood salvaged from freecycle.org
how to build a cold frame

Dont have windows? Plastic works just as well. You could clamp 4 mil plastic from the hardware store, right onto your wooden box. Just make sure its easy to open and close so you can check on your plants AND that it stays relatively air tight when you close it back up. We’ve even built a wooden frame to staple plastic on, and then clamp onto the cold frame.

Cold frames are easy, just about anything that will retain humidity and keep out damaging, drying winds and pesky animals, will do. Even something like this milk jug cloche. Just spinkle some seeds on the ground, cut the bottom off a milk jug and place it over the seeds. It really works well!
milkjug cloche cold frame

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