Extend the Growing Season with Cold Frame Gardening

Using Cold Frames for Gardening Gives You a Head Start on the Season

Extend the Growing Season with Cold Frame Gardening

By Sue Robishaw – Whether we blame it on El Niño or the gods, chaotic weather is too often a part of the gardener’s life. While this makes life more interesting, it makes gardening — even cold frame gardening — more challenging. We can rant and rave and complain about the weather, or we can simply work with whatever we are given and continue to grow our food. People have been doing so for eons, through all kinds of weather, and we can do the same.

Now I’m a bit of a lazy gardener, and not much into gee-gaws and frou-frou (in my garden or out), so my garden and farm tools list are pretty simple. Yet I grow most of the food we eat, in a frost-free growing season of about 85 days (give or take a few weeks). The success is due to a number of factors, not the least of which is a diversity of open-pollinated varieties, deep mulch gardening tactics, very little digging, orneriness, and probably mostly because seeds grow in spite of, not because of, what we do. And one of the more important strategies I use is cold frame gardening.

Not Fancy, but Functional

Our cold frames are not fancy, nor expensive, they are simply functional. And I wouldn’t want to garden without them. They allow me to plant seeds too early in the spring (such as carrots and greens). They let me transplant into the garden those things I started too early inside (they’re ready to go but the weather isn’t). They give a protected start to squash and cucumbers, and tomatoes and peppers when the spring sun is cold and the clouds never ending. And in those summers that never warm up, they allow us to grow, all summer, against odds and reason, those crops which demand warmth. Then in the fall, when the early frosts drop in on us, we can turn again to the lowly cold frame to protect those peppers or melons a few more days, or weeks, or maybe even another month. The result is more food in the better years, and some food even in the worst years.

If you are interested in cold frame gardening, then you’ll be pleased to learn you can easily make the frames out of scrap and scrounged materials. Using low-cost construction techniques, they take their allotted time to make but can last years if they are made well, and taken care of. Make your frames so they can stack, one on the other, as high as you need them. The cold frame can have a varied life in the garden. It starts all by itself protecting the early carrots and greens. When they are on their way and the weather has settled a bit it moves over to protect the squash seeds soon to be seedling. As the squash grows another frame is added on top of the first. Finally, the squash are ready to be on their own and those frames are taken away to be added to the frames around the peppers. Then more frames are added as the peppers grow. Finally, the occasional pepper crop becomes a yearly pepper crop, even in our difficult pepper climate. Meantime the tomatoes are well on their way and have outgrown their frames, which are removed and stacked aside for the summer.


Constructing Your Frames

To make your cold frames, start with whatever used windows you can get. If they are painted, scrape all the paint off that you can (we use an inexpensive mixture of raw linseed oil and gum turpentine, two to one ratio). Then build your frames to fit your window.

For wood use what you have. We have one set of frames which are made of poplar, probably one of the least recommended woods for outdoor use, but it was what we had. Those frames have been around for more than a dozen years, and are still in good shape. The trick is to store them inside when not in use; or stack them off the ground, each one crosswise to the one below it, in a well-ventilated area so they can dry easily. Our second set of frames is made of cherry, oak, maple, ash – pretty fancy wood for cold frames but we salvaged the boards from used pallets. It was a lot of work, but fun too, and nice to be making use of something which would have been trashed.

If the wood is thick enough you can screw the boards directly to each other to form a box (drywall screws work great for this). If not you will need to make 2” x 2” pieces to go in each corner to screw the boards into. Even with ¾” boards, we found the 2” x 2” pieces help to give rigidity to the frame (you’re going to be picking them up and moving them a lot). Drill holes in your boards so the screws just go through them. The 2” x 2”s in opposite corners can stick down an inch to help align and stabilize the frames when they are stacked. The other two 2” x 2”s should be flush with the bottom. (If all four 2” x 2”s stick down it makes it harder to stack the frames, especially if they warp at all).

Don’t Forget the Windows

You can make the wooden frames so that the windows sit on top of the wood all the way around if your window frames are flat on the bottom. This is simple, but the problem is when you prop the window up it will have a tendency to slip off the back side of the frame. We solved this in two ways.

The first frames we made so that the window sits inside the frame, flush with the top. We simply set the 2” x 2” corner pieces down the thickness of the window frame. Make your wooden frames a bit larger than the window to allow for warpage of the wood and swelling when it rains (if you don’t you won’t be able to get the window down inside it). This design is not really weather tight but that doesn’t seem to be a problem. And when you prop the window up it won’t slip off the back.

The second set we made we had a supply of aluminum framed storm windows to use. They were thin and not as sturdy as the wooden framed windows so we used a different design. The backboard of each frame is set 1/2” higher than the other three boards. The wood frame was made slightly smaller than the window. So the window sits on top of the wooden frame on three sides, up against the backboard. When the window is propped up the ½” ledge keeps it from sliding off the back.

In both designs, the windows can easily be pushed up over the back edge of the frame to allow full sun, air, or rain into the cold frame. And since the windows are not attached they can be lifted right off for storage.

The aluminum framed windows are easy to lift because the edges extend over the box a bit. The wooden window frames, which sit down in their boxes, need to have a handle to lift them. Old drawer hardware works nice, as does a simple handle made of coated sturdy wire. Ease of lifting is important because you will be doing it a lot. There is probably more danger of killing your plants by forgetting to open your cold frames on a sunny day than there is by forgetting to close them on a cold night. If you are going to be gone for the day and are not sure what the weather will do then err on the side of cold rather than hot. Or you can throw an old blanket or such over the top if you are concerned about the cold. This can also be done on those especially cold nights to give extra protection for tender crops.

Sue’s peppers are busting out of their frames in late summer.
These frames contain peppers (left) and cucumbers (right) in mid-summer.
Tomatoes in cold frames in early summer (note the glass covers have been removed to reduce heat buildup)

The best thing I’ve found for propping the windows up is a 2” x4” scrap sawn to 6” long. This gives you three options for how far you prop the window open. If you want more than 6” you can just push the window off the back of the frame to lean against it from the back side.

Glass vs. Plastic

I prefer glass over plastic windows because they are heavier and not as much of a problem in the wind. I have had a window blow off a couple of times, but it is rare (just prop your windows open against the wind instead of into it if they need to be open on a very windy day). I have never had a window break in over a dozen years of continued use in the garden. Glass windows do not have to be replaced every few years as polyethylene does, and other plastic won’t last as long as glass will. Besides, it’s nice to use something out of the scrap bin instead of buying it new.

If you don’t have a greenhouse or good southern windows to start growing seedlings indoors in the spring you can make a larger cold frame outside to do the job. For many years we had a permanent cold frame gardening setup constructed of discarded windows, old cement blocks (back and front walls) and scrap boards (side walls and on top of the cement blocks.) In this, we started all of our seedlings. The tomatoes and peppers didn’t do as well as in the greenhouse (it was just too cold) but they made plants from which we got a crop year after year. For squash seedlings, it was great as you could use a shovel to transplant and didn’t have the transplant shock problems often associated with the cucurbits.

There are limits to what you can do with cold frame gardening. But if you consider your plants’ natural growing habits and don’t try to push them too far, cold frames can give a good assist. With the varying weather that has become the norm, I consider them as an essential tool in my garden. Besides that, they’re fun.

What interests you most about cold frame gardening?

Originally published in Countryside November / December 2000 and regularly vetted for accuracy.

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