Extend Your Growing Season by Building a Cold Frame

My wife asked me to build some cold frames for her so that she could start some plants earlier in the growing season. Living in the Northeast, the growing season is shorter than in some parts of the country that warm up sooner and stay warm longer. The cold frame provides young plants with increased warmth in early spring.

The basic plans for this cold frame came from the book Crockett’s Victory Garden by James Underwood Crockett (Publisher: Little, Brown; 1st edition (April 1977); ISBN-10: 0316161209; ISBN-13: 978-0316161206). This is an excellent book on gardening.

The key to the cold frame construction shown in this Instructable is the availability of old windows that could be reused as the top of the frame. This saved me from building my own top. The rest of the materials are easily available at your local big box hardware store.

Materials:

1 or more – Old Window (in
my case it was approximately 4ft x 3ft in size)

1 - 4ft x 4ft piece of ¾ inch plywood. We chose not to use pressure-treated wood as we did not want the chemicals near our vegetables.

1 - 5 3/4” Galvanized Door Pull

2 - 5 inch Strap Hinges

8 – 4 inch galvanized corner braces

1 – Package of 8x3/4 galvanized screws for the hinges and other hardware pieces where the screws may be needed.

1 – 5 ft metal garden stake (to be used for as a rest for the open top of the cold frame)

1 – Wooden stake (to be used to prop open the top of the cold frame)

Sandpaper

1 can of Primer

Tools:

Circular or table saw

Sander

Tools to scrape old paint from window

Paint brushes, etc. to apply primer

Screw Drivers

Find an old window. In my case, there is a window company a few miles from my house that is always giving away old windows for free. The windows we got were about 4ft by 3ft. We picked up four of them and ended up building three cold frames, keeping one of the windows as a spare.

You may be able to find a local window replacement company or salvage company that will either give away or sell old windows.

This must be your first step and is very important as all the measurements of your cold frame will depend on the size of the windows you are able to obtain.

Scrape or strip all the loose paint from your old window. This is a step I neglected to do early in my build so I ended up doing it after the cold frame was all put together. This is the point where it would be best to do this.

Measure your window and cut your plywood appropriately. Crockett’s plans call for ½ in plywood. I used
3/4 inch for added strength. The window I used as the top was slightly larger than 4 ft x 3 ft. I measured the outside dimension of the window and the width of the frame around the border of the window. I found that a 4 ft x 3 ft cold frame would work well and allow the outside border of the window sit on top of the plywood. My measurements were as follows (shown from top to bottom in the above photograph):

One front piece – 9 in x 48 in

One back piece – 15 in x 48 in

Two side pieces – 15 in (Back) x 36 in (bottom) x 9 in (front)

The piece at the lower right was left over and not used for my cold frame.

You will have to determine the ideal measurements for your cold frame based on the size of the used window you are able to acquire.

Sand your plywood and apply several coats of a good weatherproof primer. Your cold frame will be in contact with the ground and out in all kinds of weather. Make sure to get it into the edges as well. The primer should protect your wood so the cold frame will last more than one season.

You may wish to apply the primer to the window as well.

Once all the primed wood pieces are dry, start the assembly process by attaching two corner braces to each end of the side pieces. Make sure attach the brackets to the side pieces correctly as shown, keeping in mind that one is the right side and one is the left side.

Attach one end of the front piece to the front of one of the side pieces. Pictured above, the assembled piece is lying on its side. Once this is done, you can turn it over so that it is upright, and you can attach the other side piece to the front. Then attach the back piece to the two sides. Your cold frame should now look like a box with no top and no bottom.

Up to this point, I had done my assembly in my garage, which has a smooth and level floor. For the next steps, I moved the frame to my garden, which is a little distance from the garage. I felt it was easier to move the frame without the top than to move it fully assembled. The rest of the assembly was done in the garden at the spot where the cold frame would be located.

Place the window on top of your frame and then attach the hinges to connect the window to the frame. I used two hinges per window.

Attach the door pull to the top of the window. I put it on the right front side. That way we can stand to the side of the cold frame and pull the top up, allowing us to step toward the back as the top opens. If you place it in the center of the front, you may have to bend over your cold frame, or step into it as you open the top. This is an awkward position.

Depending on where you put your cold frame, you may need something to prop up your top when it is open. I used one of those green garden stakes. I also attached a loop of paracord to the window (not shown) so I could slip it over the top of the stake. This is to keep the top from slamming down in a breeze and possibly breaking the glass.

I drilled an indentation into the window to hold the wooden stake. You can make stakes of various sizes to adjust the size of the opening for ventilation once your plants are in there.

Repeat the build as many times as you need, and start planting.

These cold frames are just sitting on the ground, so they are movable (by two people). You can either dump soil right into the frame, move it over your existing beds, or even use window boxes inside the cold frame to hold your plants.

During the winter, you can cover the cold frame with a piece of cardboard and a tarp to keep heavy accumulations of snow from breaking the glass.