Four-season Canadian gardener, author, and educator Niki Jabbour takes us step-by-step through how build an inexpensive cold frame using an old window sash, polysheeting, lumber, common hand tools, and simple hardware in this 4-minute tutorial from Johnny's.

I think of my cold frames as year-round food factories. I use them in early spring to get a jump-start on the planting and harvesting season, and again in autumn and winter to extend that homegrown harvest by months.

A cold frame is essentially a bottomless box that captures solar energy and creates a microclimate around your vegetables. You can DIY a cold frame or buy a cold frame kit. Today I'm going to show you how I built this cold frame. Let's get started...

How to Build a Simple Cold Frame

A cold frame has 2 main parts: 1) the box; and 2) the top, also called a sash or a light. 1) The box is typically made from wood, but you can also make a cold frame using bricks, landscape pavers, polycarbonate panels, or even straw bales. 2) Tops must be clear to allow light to enter the structure. You can use an old window, a shower door, a sheet of polycarbonate, or polyethylene sheeting.

This cold frame began when I found a second-hand window frame in a thrift shop. The glass had already been removed, which was convenient as I didn't want a glass cold frame top. Glass does offer excellent light transmission but it's also fragile and can break easily. Instead, I wanted to use polyethylene greenhouse sheeting for a quick and easy cold frame top.

This window frame is 48" x 30". I began by cleaning the frame to remove any debris and dust. I then cut the polyethylene sheeting to size and stapled it to the window frame, top and bottom, for a double-glazed cold frame sash.

We then switched to making the box of the cold frame. We used local untreated hemlock, which is a dense rot-resistant wood and the same wood I used for my raised beds. You can also use cedar, of course, or another type of wood.

The box was built to match the size of the window frame, so its footprint measures 48" wide x 29¼" deep, as you have to take the angle of the top into account. You can of course make a frame any size you like. Many of the frames I've built in the past were 3' x 6' with cut-to-size twin-wall polycarbonate tops. Where I have this window frame, however, I'm building the cold frame box to match.

Most cold frames are built to have angled tops; this allows increased light into the interior of the structure. The back of this frame is 15" tall and the front is 8" tall, so there is a slight slope. You may wish to use a steeper slope for your cold frame, but I find that low-angled cold frames work great. The slope side, no matter which type you use, should face towards the south for maximum light exposure.

We cut the lumber into the lengths needed to build our cold frame and began to assemble the bottom layer of the box. The front and back boards are 44" long and the side boards are each 27" long. These were screwed together using 3½" screws.

Next, we added the top layer of the box, which consists of a) two angled boards to create that angle for the top; as well as b) a backboard. The backboard is 48" long; and the angled boards measured 27" along the bottom and 7" tall at the back the backboard. As you can see, it is also cut at an angle to accommodate the angle of the cold frame.

Once the box was assembled, we added two pieces to the inside back corners of the frame to further strengthen the structure.

It was then time to add the top. We used two hinges to secure the cold frame sash to the box, and we added a handle to the front of the top to make it easy to open and close it. The final element was to add wire to the inside of the frame to ensure that if the top blew open in a strong wind, it wouldn't blow all the way back and potentially damage the structure or the sash.

Once it was complete, we moved the cold frame into place, amended the soil, and planted hearty greens for winter.

From start to finish, this project took about 3 hours to build and place in the garden, and I anticipate it will last about 8 to 10 years, although I will have to replace the polyethylene cover about halfway through the lifespan of the frame.

Cold frames are game-changers in the food garden. They're an easy way to jump-start the spring garden and extend the harvest well into winter.

Happy growing!

Learn more about growing vegetables with Niki: 8 Great Vegetables for Beginning Gardeners • Video Series…

For more in-depth information on season extension and winter growing, scroll the menu at left to browse all our resources on this topic.