2005-09-29 / News

Extend your growing season with a cold frame

By Roger Marshall

Psst, got a few old storm windows? If you have, your plants are going to love you. Why not use them to build a simple cold frame?

This cold frame is easy to build and will help your plants harden off in spring, prolong the summer season, and give you a little more gardening pleasure.


Growing bed:

Four corner posts 4by 4by 24-inches.

Two 12-foot 6-inchby 2by 12-inch pieces.

Two 4by 2by 10-inch pieces.

Cold frame:

Three to seven storm windows

Three 12-foot by 2by 4-inch pieces.

Four corner posts 4 by 4 inches cut to suit the angle of the frame top.

Four 4by 2by 4-inch end pieces cut to suit the frame ends.

Short lengths of scrap 2by 4inch pieces as needed.

Plywood to clad frame as shown

Here’s how to build it:

1. Measure the size of your storm windows. We’ll assume the ones shown are 5 feet long and 30 inches wide. As there are five windows, we’ll make the growing bed 4 feet wide and 12 feet long. The additional 6 inches will slightly overlap the end of the frame.

2. Mark out the growing bed and measure the diagonals to ensure that it is square. If the diagonals are of equal length the bed is square.

3. Hammer four corner posts into the ground, 1. 5 inches in from each corner.

4. I like to make the bed separate from the cold frame so that when the lumber around the bed rots out it can be replaced without damage to the cold frame. But you can make the cold frame and bed supports one piece if desired.

Also if the frame is separate from the bed, it can be lifted off and placed on another bed if desired. To set the frame so that it is moveable, cut the corner posts about 4 inches below the top of the bed’s edge pieces and cut the cold frame corners to drop into the bed corners to lock the unit in place.

5. Cut two 2by 12-inch by 4foot lengths for the end of the frame and two 12-foot 6-inch lengths for the sides and nail them to your posts. That will give you a basic growing bed. At this point, you might like to dig the bed over and amend the soil to make sure it is healthy.

6. The frame is made using three 12 foot lengths of 2 by 4 at the top, bottom, and front of the structure, with shorter, 4 foot long 2 by 4s at the ends. Use scrap pieces to fill in as shown in the figure.

7. Cut plywood or barnboard siding to fit the ends and back of the frame and nail it in place. The windows are fastened with hinges at the top. If you want to insulate the back and ends of the frame, keep in mind that you don’t need much insulation. The glass will allow plants to get cool very quickly, so I suggest that you use Styrofoam or foil-faced foamboard along the sides and back to increase the insulation and to give a reflective surface.

8. You should paint the cold frame before installing the windows. I painted my frame white to reflect as much sun as possible.

After installing the windows, there will be small gaps between each window that allow air to escape when the frame heats up. To cool the frame simply prop a window open with a stick or specially cut piece of wood.

You might want to fasten a couple of pipe clips to the front of the frame to hold your prop in place so that the wind can’t blow it over.

The frame can be built in a few hours and will give you a lot of pleasure as you put early plants and start seeds in it a week or two before you can normally set them in the ground.

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