A cold frame is a simple tool for season extension.
I often want to get plants growing early in the season to give them a head start. But, I do not have a window that is sunny enough to start them indoors. My original method was to carry them in and out of my shed on a daily basis. I considered getting a small greenhouse to reduce the labor involved in starting seeds. However, I do not have the space or the inclination to spend the money on one. Instead, I began looking for simple alternative structures that I could put together easily and inexpensively. The solution was to build a cold frame.
What is a cold frame?
A cold frame is a structure that is easy to build and simple in design. It consists of a removable glass lid that admits light into a four-sided frame. The cold frame traps warmth, and is placed on the ground to protect seedlings and small plants without artificial heat.
Using recycled material to build a cold frame
We created a portable cold frame using an old window that we found in our alleyway as the lid. The frame was build using scrap wood, cut to duplicate the dimensions of the window. The cold frame is located on the south side of our property in a very sunny location. It faces south to collect as much sunlight as possible.
How to use a cold frame
As temperatures begin to rise in the spring, the lid is removed partially or completely during the daytime. This allows airflow and releases moisture build-up. The cold frame is closed at night as temperatures fall. A cold frame works wonderfully to warm the soil enough to germinate warm season plants early in the spring. In cold climates that experience hard frosts, a cold frame may provide enough protection to grow cool season plants, such as greens, all winter long.
Four Ways to Use a Cold Frame by Adrianna Vargo of Fine Gardening
How to Build Cold Frames by Sunset Magazine
Cold Frames and Hot Beds by Cornell University Extension, Chemung County
Growing Plants from Seed by S.E. Newman of Colorado State University Extension (includes a tutorial on making cold frames)