How to Build Cold Frames for Your Garden
Growing edibles outdoors in the Pacific Northwest is easy in the summer, but it is pretty difficult throughout the rest of the year without the help of protective structures like greenhouses, polytunnels, and cold frames. Without these kinds of garden structures, harvestable garden food isn't usually ready until late June or early July, but these easy-to-build DIY cold frames are a great way to get fresh, year-round produce from your own garden.
Location, Location, Location
Location is key when thinking about including cold frames into your garden design. If you plan to use them during the darker, colder, winter months, you'll want to choose a location that receives as much light and warmth as possible.
For two years, I'd been walking past the south side of our garage, observing the sunlight it received and the warmth it reflected. Not using that space for growing plants seemed like an obvious waste, but digging into the ground next to it wasn’t an option since it consisted of years of hard-packed, driveway gravel. Therefore, some kind of raised bed design was necessary, and cold frames seemed like the perfect solution to my needs.
I found a book at the library with lots of DIY garden projects in it, including the blueprints and instructions for these cold frames. This were the first construction project that I completed entirely by myself (from finding the design, picking up supplies at the hardware store, and building with power tools) and I’ve gotta say, I was feeling pretty darn capable and satisfied with myself while I worked on them in the garage in January, bundled up in a parka, gloves and a tuque.
Tip #1: Libraries are great resources for free information about building projects.
Tip #2: Don't be afraid to ask for assistance from hardware store employees. Not only can they direct you to what you are looking for, but they're great sources of information, tips, and suggestions.
Tip #3: If you've never used power tools before, make sure you know how to handle them properly before you dive into your project. Safety first! If you don't have your own tools, approach neighbours, friends, and family members to see if you can borrow some.
These instructions are what I followed to make our cold frames. Not all of our cold frames are uniform in size because I made use of some plywood pieces we already had one hand. Once you've got one cold frame under your belt, you'll have a better idea of how you can adjust the measurements and design to your liking.
Materials for one cold frame:
- a 8′ x 4′ piece of untreated plywood. I chose untreated to avoid the heavy chemicals that are on treated wood.
- approx. 50′ of 2x2s
- poly plastic ( a 4.5′ x 5.5′ piece for the lid) and more if you want to line the inside with it.
- 2 hinges
- staple gun and staples
- corner brackets (optional)
- black and white paint (optional)
- Cut the plywood according to the measurements listed in the drawing above. The 8′ x 4′ piece of plywood provides everything you need for the walls of a 5′ wide x 4′ deep cold frame. The cold frame sits 2′ high at the high end and 1′ high at the front, low end.
- Cut pieces of the 2x2s to fit inside each interior corner of the cold frame. These will provide strength and stability to the cold frame box. Screw the plywood walls into these interior corner 2x2 pieces.
- Cut the rest of the 2x2s to mirror the shape of the top of the cold frame. These will form the frame of the cold frame lid. They are screwed together at the corners. If desired, you can attach corner brackets to the corners of the frames as well for extra strength.
- Save any 2x2 scraps left over to use as side handles (to make transporting the cold frame easier) and as a lid handle.
- Connect the lid frame to the cold frame two hinges placed evenly along the backside (high side) of the cold frame.
- Using a staple gun, attach poly plastic to the framed lid of the cold frame. Glass can be used as well if you want to get creative. It is very important that the lid allows light into the cold frame.
- If desired, paint the interior of the cold frame white (to reflect sunlight onto the seedlings and plants growing within it), and the exterior black to absorb sunlight which will help keep the cold frame warm.
- If desired, you can also line the interior of the cold frame with poly plastic to protect the wood from interior moisture damage.
Filling Your Cold Frame
Once your cold frame is finished, move it (empty) to wherever you have decided it will live. Trying to move a cold frame full of soil would be very difficult, so don't fill it with soil until it's in its final resting place.
Since there are no bases to the cold frames, I laid cardboard down beneath them first (cardboard is a good mulching material that will break down and contribute to healthier soil). After that, I layered the interior of my cold frames with old straw (another great mulching material), compost, and topsoil, and then planted some kale and bok choi seeds right away.
As you can see from the photos, our greens grew great in these cold frames – much more robust than those that got planted in trays in our polytunnel because their roots had so much more room to spread out and absorb nutrients.
In addition to using the cold frames to grow winter greens in and to start spring seedlings in, we also found they were great for summer tomatoes because of the warm location and the shelter of the over-hanging garage roof.
For those of you looking for new gardening projects or desiring ways to grow your own salad greens throughout the winter, I highly recommend this easy, DIY cold frame project!