How to Build a Cold Frame

Follow these easy steps to extend your garden's growing season.

Cold frame

A cold frame can extend your growing period by two to three weeks at each end of the season. Cold frames can be made from old storm windows, spare panes of glass, or other recycled materials.

Illustration by Roger Marshall

Content Tools

In Garden Projects: 25 Easy-to-Build Wood Structures and Ornaments (The Countryman Press, 2015), Roger Marshall provides step-by-step instructions on how to create a variety of simple DIY additions to any outdoor space. Use these project ideas to add a practical, aesthetic element to your backyard or to improve your garden production. Marshall has years of construction experience, and has developed projects that can easily be completed using materials from any local hardware store.

You can purchase this book from the GRIT store: Garden Projects.

Building a Cold Frame

A few years ago, I was given five wood-framed storm windows, each 30" wide, and decided that they would make a great cold frame for my garden. As the growing beds were already 4 feet wide and the windows were 5 feet long, the cold frame’s back height of 3 feet was simple to calculate (3-4-5 triangle). I built two triangular ends and a rear section and screwed the three parts together easily, after which the storm windows were simply set in place.

Tools:

• Handsaw or rotary saw
• Screwdriver or hammer
• Tape measure

Materials:

• Two 4-inch x 4inch x 4-foot pressure-treated posts for the back corners

For the ends:

• Two 2-inch x 4-inch x 3-foot boards
• Two 2-inch x 4-inch x 28-inch boards
• Two 2-inch x 4-inch x 22-inch boards (Tops will be trimmed to suit the slope of the triangle.)
• One 2-inch x 4-inch x 4-foot board for the base
• One 2-inch x 4-inch x 5-foot board for the hypotenuse
• Scrap barn board or siding to cover the ends, or one 1/2-inch x 3-foot x 4-foot marine-grade plywood sheet, cut in half along the diagonal

For the back:

• Two 2-inch x 4-inch x 12-foot boards for top and bottom rails
• Six to ten 2-inch x 4-inch x 3-foot boards for the supports for the top and bottom rails. (Spacing the supports 24 inches apart requires six supports, and spacing them 16 inches apart requires ten support posts.)
• Scrap barn board or siding to cover the sides, or one 1/2-inch x 3-foot x 12-foot marine-grade plywood sheet
• Five 30-inch x 5-foot wood-framed storm windows

Fasteners:

• Either 16P nails or 3-inch galvanized or ceramic-coated exterior screws for the main framing
• 1-1/2-inch 6P or 8P galvanized exterior nails for installing the plywood.

Time:

I built my cold frame in about 8 hours but your actual time will depend on the type of windows or glazing that you use.

Method: 

1. Sink the 4-foot posts 1 foot deep into the ground at the two back corners of the bed.

2. Build the rear frame. Lay the top and bottom rails out on a flat surface and screw or nail the support posts in place at 16-inch or 24-inch intervals along the rails.

3. Build the end triangle frames. Make sure the tallest post is the same height as the rear section (nominally 3 feet) with the triangular section tapering to nothing at the front. Space the supports and cut them to suit the end angle before nailing or screwing them in place.

4. Erect the ends and rear sections and nail or screw into place. This frame will now look like Figure 16-1. (This frame has four windows instead of the five that I built my frame with.) 

5. Clad the frame with siding. Size your siding to extend below the side of the frame in order to cover the air gap between the sections and the raised bed. Figure 16-2 shows progress.

6. Set the windows in place. They do not need to be hinged, but you can install two 3-inch hinges at the top of each window to ensure the windows stay in place. A simple stick pushed into the ground in front of the frame will serve to keep the frame open.


Reprinted with permission from Garden Projects: 25 Easy-to-Build Wood Structures and Ornaments by Roger Marshall and published by The Countryman Press, 2015. Buy this book from our store: Garden Projects.