Quick Instructions: Wood
- Build a box out of wood, concrete blocks, hay, or other material.
- The sides can be at a 45-degree angle to collect maximum solar heat.
- Place a clear lid of plastic or glass on top of the frame.
- Make sure there are no air leaks.
- Set your cold frame in a south-facing direction.
Quick Instructions: Low Tunnel
- Push both ends of 1/2″ PVC into the ground to make a hoop.
- Space another hoop 8′ away from the first.
- Connect the hoops with two 8 foot 1×2″ wood strips.
- Cover with plastic.
- Weigh plastic down with concrete blocks, rebar or sandbags.
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.
How to Build Wooden Cold Frames
Some key things to think through when you’re considering how to build a cold frame with wood.
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 a simple south-facing cold frame built with scrap wood and salvaged windows.
Size and shape were 100% determined by the location and materials at hand. It could use some soap and water, but overall it blends nicely with the garage.
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 you can tuck your plants in that retains humidity and keeps out drying winds will do. Even something like this milk jug cloche below. Just sprinkle some seeds on the ground, cut the bottom off a milk jug or 2 liter bottle, and place it over the seeds. It really works well! Just make sure to bury it a little so it doesnt blow away.
Low Tunnel Cold Frames
Another way to build a cold frame is with a low tunnel. I use these personally because I need to cover quite a large square footage to overwinter my nursery plants. Plus, it’s so much cheaper. Your goal: To create a plastic-covered environment that traps heat and humidity and doesn’t blow away. PVC holds plastic up. A 2×4 frame holds the PVC up. (or you can just push them deep into the ground). Heavy blocks keep the plastic on. Its as simple as that. BUT there are a few pointers.
Use 1 or two crossbars (1×2″ furring stips work) taped from one hoop to another (plastic packing tape works) This keeps the plastic ’round’. So when it rains or snows, it falls over the side rather than sinking the plastic. Also. You should poke small holes in the top of the plastic to allow water to come through.
The most durable plastic that holds the highest amount of heat and humidity is string reinforced plastic. Or, if you have mild winters or you’re just trying to extend the spring or fall season, you can try two sheets of the cheap plastic. (cheap plastic rips apart through harsh winters)
You can build a cold frame right on top of your garden bed to get a jump on the spring growing season, or to extend into fall.