Cold frames are among the simplest and most useful ways to extend the growing season. As James Theuri, University of Illinois Extension educator, notes in an earlier post, they are basically a box with a covering to let light and heat in during the fall and winter months. If money is no object is your gardening, there are lots of places to buy kits, but if you would like to save a little money and are willing to do a little scavenging and work, it’s pretty easy to find the materials you need.
There’s nothing like an eagle eye during trash day to scrounge up wood and glass. Windows and other sources of glass and lumber are pretty pricey at the hardware store but they seem to routinely find their way to landfills anyway. If you’re looking online, Craigslist, freecycle and a number of other places post free stuff all the time. There are just a couple of things to bear in mind as you’re looking around.
The length and width of the box can be adapted to any glass source and garden size, so it might make sense to find your top first and then cut lumber to accommodate the size of the light. (Old windows are a good choice if you can find one for cheap or free, although they are not perfect – the frames can accumulate rain and they really weren’t designed to be sideways.) On the other hand, there is near-universal agreement that you want the box to taper down in size from back to front (and that the box be facing south) to make the most of winter sunlight. Eliot Coleman recommends a 12-inch board for the back of the box and an 8-inch board for the front.
There are lots of plans for cold frames online, but they tend to be a bit more complicated than is necessary. (Nevertheless, if you like a blueprint, you can find some here and here.) Lots of people blog about their cold frames and extending the season and it’s definitely worth sticking “cold frame” into a search engine and learning about different people’s experiences.
For example, the folks at Lunaria Gardens have a great explanation for how to build the easiest cold frame ever. Savvy Gardener has a nice rundown of the many protective options available for extending the season – some that are even easier than a cold frame (although you probably want to keep a close eye on something like a glass covering over a plant). This video also features a couple of different cold frame designs and there are a few other videos related to it to choose from after watching.