Celebrate the culture of agriculture & share skills (Growing! Cooking! Eating!)

The following 101, on building a cold frame, comes from HOMEGROWN member Urban Overalls, the city gardener, home cook, and chicken keeper behind the eponymous blog. Thanks so much, UO, for sharing your cold frame know-how with HOMEGROWN and please keep hammering out the good ideas!

Cold frames. They are the workhorses of my garden. Every year I pull them into service, both in the early spring and then again in the fall. They alone allow me to extend my growing season from late February into at least mid-December. That’s pretty darn good for living in USDA hardiness zone 5, where we typically would be cleaning out our garden beds in September or October, depending on when we get our first freeze.


If you are new to gardening, a cold frame is a transparent roofed structure that protects young plants from cold weather. Ideally, a cold frame should be situated in a sunny location with good southern exposure. The structure keeps tender plants safe from harsh winds while providing exposure to sunlight through the transparent roof. It also helps retain radiant heat, similar to a greenhouse but on a much smaller scale.


Besides extending the growing season, one of the benefits of a cold frame is that you can readily build your own, using either new materials or items you might have on hand from previous home projects. All you need are some basic carpentry skills and a short list of materials.



» old window frame or sky light window, with glass intact

» recycled cedar, cypress, or redwood, or other untreated lumber

» wood posts (optional)

» door hinges (at least two per cold frame)

» screws



» screwdriver

» saw

Urban Overalls' cold frame, with the roof open and veggies planted inside.

The same cold frame, with the roof closed and covered in snow.

Hooray for cold frames! Underneath all that snow, the greens are warm and thriving.



Remember to stay away from pressure-treated wood and railroad ties. These typically contain chemicals, such as pentachlorophenol or creosote, that release vapors toxic to plants.


In building your cold frame, you want to keep the size manageable. Your window (or whatever transparent material you’re using for the roof) will determine the width and length of your frame. For example, if your window is 2’ x 4’, the cold frame box will be 2’ wide and 4’ long. 


As for the height, build the back of the cold frame 6” higher than the front. This will created a sloped roof, allowing water—and, in northern climes, snow and ice—to run off your cold frame. So, if you make the front of the cold frame 12” high, the back should be 18” high. Remember that you do not need to build a very tall structure. You want to be able to comfortably reach inside the cold frame when planting and harvesting your cool-season produce.


On to building! First cut two posts to 12” and two to 18”. These will be the corners of your cold frame. Next, cut your lumber to 2’ and to 4’ lengths. Screw the wood to the posts to form a 2’ x 4’ rectangle. NOTE: if your lumber is sturdy and not warped, you can skip the posts and simply screw the lumber together to form a rectangle.  


Cut the 2’ sides at an angle with a saw so that one end is 18” and the other end is 12”. Once you’ve got your frame screwed together, lay the window on top. Place the hinges on the back of the cold frame and the window frame and screw into place on the high side first (the 18" side rather than the 12" side). By placing the hinges on the high side, you will be able to open the structure and reach comfortably inside.


Congratulations! You are now ready to set your cold frame over a garden bed—or to plant a new bed inside. For maximum season extension, place your cold frame in a location that receives at least 6 hours of sunlight per day and fill it with cool-season crops, such as spinach, lettuce, and radishes. These will perform much better in fall and late winter/early spring weather than warm-season crops, and you’ll enjoy the fruits and veg of your labor for even more of the year!



Got a question for Urban Overalls? Or a cold frame tip of your own to share? Post it below and keep the conversation rolling. You might also be interested in the Raised Beds 101 and Anne’s Self-Watering Container 101. If you’re looking for more on season extension, check out the Fall Planting 101, Winter Planting 101, and Hoop Houses 101. When (or if) you do pack it in for the year, be sure to give the Garden Winterizing 101 an ogle. For year-round gardening tips, check out the Selecting Seeds 101, the Garden Planning 101, and Karin’s Companion Planting 101. And don't miss Urban Overalls' Green Tomato Wine 101. You can always find more things to plant, grow, cook, preserve, make, craft, and saw in the HOMEGROWN 101 library


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Just a few suggestions -

If you can find glass shower doors, they are made of safety glass, and if they break, it is less likely to cause harm.

you should also provide means for holding the door securely, whether it is closed, open, or venting, in order to prevent damage from the wind. The outside edges should be banked so that there is no access for animals or insects, and the sides should be low enough to access the interior easily. Finally, the wood in contact with the soil should be rot resistant, such as cedar or locust or redwood, or else easily replaced - it will only last a few years before the integrity is compromised.

I use old or warped exterior doors (R14 insulation in exterior doors) for the front and back and old aluminum storm doors for the top. You can see from the above photo that the storm door fits neatly into the space without cutting. The ends are made from steel door cutouts that have been removed from the exterior door slab to allow a window to be installed.

I love the idea of using old doors and windows...just be careful about lead content in old paint and line the inside for edibles...

in our area lead paint is also an issue on many of the homes.  Home Depot or Lowes both sell tiny lead paint testers.  I think they are relatively inexpensive and will let you know if there is lead in the paint on any window you might find

Linda Turner said:

I love the idea of using old doors and windows...just be careful about lead content in old paint and line the inside for edibles...

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