I had planned to build a cold frame and carefully document the process for this feature. I told Joel I was going to build a cold frame for this feature. I even got a hold of some very nice rough-cut cedar for the frame. My wife was happy that I was finally going to do something with those sliding glass doors that I had scavenged seven or eight years ago and have been stashed in one corner or another of the basement ever since. It was going to be the Cadillac of cold frames. Well, perhaps the Monte Carlo of cold frames.

A couple of days of cold, wet weather and rapidly approaching work deadlines have put the nix on the whole project. But this got me thinking, you don’t need to learn to build the Cadillac nor even the Monte Carlo of cold frames—you need to learn to build the rusted out Geo Metro that you have to push start of cold frames. Because the wheels on the Geo Metro go around just like they do on the Cadillac.

What the hell is a cold frame?

A cold frame is a growing season extender. You use a cold frame to maintain a pillow of air around delicate plants that is marginally warmer that the ambient outdoor temperature. In the Spring (or even late Winter) you use it to start your cabbage, roma lettuce and broccoli. In the Fall you use it to continue to grow leaf lettuce, spinach, arugula and carrots to fill your salad bowl far into November.

A cold frame is also a buffer for the lag between solar-winter and temperature-winter. Solar-winter is over in mid-February but temperature-winter doesn’t always want to cooperate and warm up. Many plants respond to the lengthening days (most importantly members of genus Allium i.e., leeks, rocambole garlic, onions and chives) but if it’s too cold out they will wait. If they’ve been overwintered in a cold frame you won’t have to wait.

So what is a cold frame? It is a low box or rectangle made of some insulating material with a translucent top that is stiff enough to not sag under a layer of snow. Easy, eh?

To build one the first thing to do is scrounge up a top. Glass is best (until you fall and put your hand through it) but plastic will work and the closer to transparent the better. Dumpster finds are the order of the day.

Next you’ll have to material for the sides for your box. Insulating quality counts here. To help you could dig a pit around six inches deep and roughly the dimensions of your soon-to-be-completed masterpiece. Soil is an excellent insulator.

Some additional care is required in choosing the materials for the sides. Will this be a permanent feature in your space? If so you’ll need to choose materials that will resist rot, red cedar or redwood are good choices. (If you must use wood please don’t use treated lumber. It can leech Very Bad Stuff into your soil.) But you can also use masonry block or clean, used brick.

If it will be a transitory feature use whatever will work. I’ve seen excellent performance with hay or straw bales. They will fall apart after a year but then you have some excellent compost started.

Many cold frame designs feature an angled top. It isn’t necessary (and is really there to promote rain water runoff) but if you do integrate this feature into your design insure that the low side of your cold frame faces to the South.