A cold frame is an enclosure used to protect plants from cold weather. It has a transparent top to allow sunlight in to warm the plants inside, acting like a small greenhouse. Cold frames aren’t used during warm summer months (it would be too hot for plant growth), just during cooler times of year. They help gardeners get a jump on the upcoming growing season and to grow things later into the fall. Select a location for your cold frame—a south-facing side of a building is best.
Note: When using an old window, make sure it doesn’t contain lead paint or pressure-treated wood. When purchasing wood, measure around all sides of the window; that is the total length of wood you will need. For example, if the window is 3’ (91 cm) long and 2’ (61 cm) wide, you would need 10’ (305 cm) of wood (3 + 3 + 2 + 2 = 10).
MATERIALS
Pieces of redwood or cedar: For this window, we obtained one piece of cedar 1" x 12" x 8’ (2.5 x 30 x 244 cm) for the back and two sides, and one piece of cedar 1" x 8" x 2’ (2.5 x 20 x 61 cm) for the front.
Straight edge
Pencil
Circular saw
8 corner wood braces
32 wood screws
Screwdriver
2 hinges and screws
1 old glass window (this one measured 21" x 27" (53 x 68.5 cm)
10" to 12" (25 to 30 cm) stick
1. Start making the box frame. Because the window will be tilted down in front slightly, the two side pieces of wood will be cut at an angle. The front of the side pieces will be the height of the front board; the back of the side pieces will angle up to the height of the back board. Measure and mark each side piece accordingly. Use a straight edge to draw a straight line from this mark to the top of the other end, creating an angled piece of wood. (Fig. 1)
2. With adult assistance, use a circular saw to cut each of the four pieces of wood along the line you drew. (Fig. 2)
3. Position each piece of wood at a right angle to the next to create an angled box with the tallest piece of wood as the back of the cold frame. Fasten a corner wood brace 1" (2.5 cm) from the top and 1" (2.5 cm) from the bottom inside each corner. Use the wood screws and a screw driver to attach the pieces to each other. (Fig. 3)
4. Attach the hinges to the outside, top back of the frame, then attach the window to the hinges. (Fig. 4) Place plants inside the cold frame. On warmer or sunnier days, use a stick to prop the window up a bit so it doesn’t get too hot inside and bake your plants. (See photo on page 76.)
DIG DEEPER!
EXTEND THE SEASON
Making a cold frame can be as simple or as complicated as you wish to make it. We are doing a very simple version of one here, and once you get the idea, you can experiment with building something different.
Unless you live in an area where you can grow year-round, you might want to investigate how to grow things earlier in the season as well as later in the season. This is called “season extension,” and your cold frame can help you do it.
Because of the window acting as a lid, rain won’t be able to enter the cold frame. This means you are responsible for watering any plants inside. During very cool months, many plants are dormant and don’t need much, if any, water.
