One complaint you often hear about cold frames is “Mine’s not big enough.” Well, you can’t say that about this one. It utilizes a cast-off storm door for the glazing and provides nearly 20 square feet of planting room.
This design is based around a standard aluminum storm door—the type that’s mounted in a frame—but the details are easy to modify to accommodate other types of doors or casement, slide-by, double-hung or storm windows.
Most storm doors are made to fit 32-by-80-inch or 36-by-80-inch entry doors. Because sizes can vary, I don’t provide exact dimensions here. Measure your storm door frame—outside edge to outside edge in both directions—and build your cold frame based on those measurements. Your goal is to have the outside edges of the storm door frame flush with the outside edges of the cold frame box.
- 3 10-foot pressure-treated 2×10s
- 1 6-foot pressure-treated 2×10
- 3 8-foot pressure-treated 2×2s
- 32- or 36-inch storm door
- 16d galvanized nails
- 3-inch and 4-inch galvanized screws
*All lumber should be pressure-treated material rated for ground contact.
To create the sloped sides (A) of the box, start by marking a diagonal line that equals the width of the storm door frame, on a 2×10 (see drawing detail). Cut the angle using a circular saw and straight-cutting jig.
Cut the lower side pieces (B) to length. Use a few nails to tack parts A and B together; you’ll make more secure connections using 2×2 cleats later on.
Set your circular saw to cut a 15-degree bevel. Rip the edge from a 2×10 for the top board for the back of the box (C). Use the straight-cutting jig or table saw for a straight, accurate cut. Cut the lower back piece (D) to length and tack it to C with a few nails. With your saw set at 15 degrees, rip the angle on the top of the front board (E).
Courtesy Bruce Kieffer
Use 4-inch galvanized screws to assemble the box as shown above. Take care to align the tops of angled ends (A) with the tops of the beveled front (E) and back (C) to create a flat plane for your storm-door frame. It’s OK for your frame to be uneven at the bottom, but not on the top where the storm door frame rests.
Cut the 2×2 cleats (F, G, H) to the lengths needed for them to join the boards they connect. Secure them to the corners and all sides of the box with 3-inch screws, as shown. Space the cleats along the front and back so they’re directly across from one another.
Cut the intermediate dividers (I) to fit snugly between the front and back of the box, using the 6-foot 2×10. Install the dividers by fastening them to the sides of the 2×2 cleats.
Position and level the cold-frame box. You can dig it into the ground a few inches or let it sit directly on the ground. Measure the diagonals to make sure the box is square, and adjust the box as needed. With the assistance of a helper, set the storm door (J) in place. Make any necessary adjustments to ensure that the door opens and closes properly; then screw the door frame to the frame of the cold frame box.
Note: The top and sides of the door are supported by the door frame, but the bottom is not; screw a pair of 2×2s (K) to the cold frame box to support it.
Safety, Safety, Safety
Whenever you use something like a storm door in a novel way, safety becomes a concern. Storm doors were created to stand upright, not lie horizontally, so keep the following safety issues in mind.
The glass in most storm doors is single strength (to keep the weight down) and untempered (to keep the cost down). If you live in an area subject to hail, if the cold frame is near trees that drop branches or nuts, or if it’s in an area where there’s lots of activity, consider replacing the glass with plexiglas. You may also want to cut a piece of styrofoam and keep it on hand to secure over the door in the event of an impending hailstorm or hard freeze.
A gust of wind can catch a partially open door and swing it back with great force. Use limiting chains to prevent this. Make sure they’re long enough to allow you to open the door far enough to work comfortably and safely. And use a pair of stout 2×2s (one on each end) to keep the door propped open while you’re working.
The door is heavy and the edges are sharp. Prop the door up solidly when working in the cold frame. You can also install a pair of piston closers (one on each end) and use the opening clips on the closer rods to hold the door open.
Teach your kids that a cold frame isn’t a playhouse, doghouse or plaything. Unless they’re working alongside you, kids should stay clear of cold frames.
Using Your Cold Frame
When you use your cold frame, as well as where you position it and how long you use it, are all based on your growing zone, what you plant and your gardening goals. In most areas, you’ll gain four to eight weeks of growing time by using a cold frame to start plants and harden off seedlings.
The ideal temperature in a cold frame is 65 to 75 degrees F during the day and 55 to 65 degrees F in the evening. Keep a cheap thermometer in the box (preferably out of direct sunlight) so you can monitor temperature. To release heat on a sunny day, prop open the door slightly (or open one of the sliding windows). If a freeze is forecast, cover the box with a quilt, leaves or hay.
For maximum sun exposure, orient your cold frame facing south. Some people paint the inside of the cold frame white to reflect more sun and prevent seedlings from overreaching in one direction. A cold frame helps keep moisture within the confines of the box, but it also prevents rain from getting in, so monitor the moisture content.
About the Author: Spike Carlsen is the former executive editor of Family Handyman magazine. He’s been involved with wood and woodworking for more than 30 years and is the author of Woodworking FAQ (Storey Publishing, 2012) and A Splintered History of Wood (Harper, 2008). He lives in Stillwater, Minn.
This article is excerpted The Backyard Homestead Book of Building Projects (Storey Publishing, 2014), by Spike Carlsen. Project illustration by Elayne Sears. Plan drawings by Bruce Kieffer. Used with permission of Storey Publishing.