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Extend your growing season with a cold frame

Oct 1st, 2013 | Category: Skills

by Samantha Schuller

If you were grumping and muttering under your breath this summer at your unproductive melon vines, short tomato season, and stunted peppers, now is the time to start gloating about our Pacific weather. We here in the Northwest are blessed—that’s right, blessed—with usually mild winters, which means that we get a growable winter where others in America are hopelessly buried under snow until spring thaws them out.

Materials include plywood, single pane windows and torque screws. PHOTO BY SAMANTHA SCHULLER

A cold frame is an enclosure that insulates your plants by up to 10 degrees, keeping them above freezing most days. Many cool-weather crops can tolerate light frost, and some can even survive hard freezes.

You will need a garden bed, lumber that is the length and width of your bed, scrap pieces to form the corner joists and window-supports, and as many single pane windows as you need to cover the top of the structure. All of these things can be had for a pittance at salvage yards and re-used materials stores like The Re-Store and Skagit Building and Salvage.

Cut the plywood into four pieces fitting the necessary dimensions, then assemble your rectangular frame. PHOTO BY SAMANTHA SCHULLER

I found some plywood pieces at the Habitat for Humanity store in Mount Vernon which were already cut to the perfect size for my garden bed. You may end up using different materials, but the basics of construction will be the same. Materials include plywood, single pane windows, torque screws, and a circular saw or hand saw and electric drill gun. (See the sidebar for specifics.)

Cut your 2×2 into four 12-inch sections, which will be your corner joints, and eight 6-inch sections, which will be your four slide protectors and four window braces.


Next, screw the four corner joints (2x2x12) onto your two 8-foot sections of plywood, leaving a lip the width of the board you will be joining at the end. Now assemble your rectangular frame, minimizing the number of screws you use while still making a sturdy structure. Remember that you will be taking this apart in spring!

Add your slide protectors and window braces. The slide protectors are perpendicular pieces attached to the side of the frame which will be facing south. When you vent the frame on sunny days, they will keep the windows from falling off. The window braces help keep the windows from slipping in when you lift them up. They might be unnecessary if you are using thicker wood for your frame or very light windows that you won’t drop. Two are screwed flush to the level of the inside of the frame, and two are screwed to the outside of the frame, an inch higher than the inner ones. These just help guide the window into place and prevent the window from being knocked off accidentally.

Congratulations! Construction is complete.

Grade your garden bed so that it slopes towards the south. Your cold frame will rest on top of this slanted surface so that it is tipped toward the fall and winter sun. PHOTO BY SAMANTHA SCHULLER

Now grade your garden bed so that it slopes towards the south. Your cold frame will rest on top of this slanted surface so that it is tipped toward the winter sun. If you are working around established plants and can’t rake across the whole bed, just grade the border where the frame will rest by digging the southern edge low and building up dirt on the northern edge. Dig out the east and west edges, move the cold frame in place, and fill in around the sides.

You will need to open the cold frame during the day when you see condensation on the glass, or whenever the temperature inside is warmer than about 65 degrees. Remember, you are planting cool-weather crops in this frame, many of which will bolt if it gets too hot!

Cold frames are easy to assemble, and well-worth their limited expense in the value of produce you can reap from them all winter long. By using scrap lumber and discarded single-pane windows, these inexpensive structures will bring you fresh, local produce through the winter and give you a jump start on planting in spring.

The completed cold frame. PHOTO BY SAMANTHA SCHULLER

Some tips? Use torque screws, which will be easier to take out in spring. Don’t use particle board, which will get soggy and fall apart. Be sure the windows you choose are light enough for you to carry; you will be taking them off to weed and harvest.

Recommended reading for additional information includes Steve Solomon’s Growing Vegetables West of the Cascades and Eliot Coleman’s Four-Season Harvest.

Samantha Schuller is a writer, mother, and gardener living in Arlington.

Materials you will need

These materials can be had for a pittance at salvage yards and re-used materials stores, or talk to friends and neighbors about materials they may have to share.
• Two 8-foot sections of 12-inch wide plywood
• Two 3.5-foot sections of 12-inch wide plywood
• One 8-foot long 2×2, cut into 12 pieces
• Single pane windows to cover your frame, at least 40 inches wide
• 40 1½ -2-inch torque screws
• Circular saw or hand saw
• Electric drill gun


Try planting vegetables such as spinach, loose-leaf lettuce, head lettuce, broccoli, sprouting broccoli, carrots, rutabagas, mustard greens, parsnips, arugula, brussel sprouts, or kale. All of these veggies have some degree of cold-hardiness. Also, visit your local gardening centers and neighbors to see what information they can offer for cold-season growing, or check out resource books.

One Comment to “Extend your growing season with a cold frame”

  1. Maria H says:

    We are definitely going to do this! You made this very manageable for us!

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