No matter where gardeners live, the growing season is never long enough. It wouldn't be hard to extend the growing season a little in the spring by constructing a cold frame. Many gardeners use a cold frame and have great lettuce and onions, for example, weeks before anyone else.
A cold frame is nothing more than a glass or plastic covered box outside that stores the sun's heat, all the while giving the gardener some control over temperature through the use of ventilation.
The gardener can start seeds in the warm daytime temperatures that the mini-greenhouse provides and the cool nights inside the cold frame allows seedlings to develop healthy, rugged growth in about six weeks.
The size of the cold frame is dependent on the amount of the lettuce and onions you want. However, a 4 feet by 4 feet box is plenty large enough for an average family of 4 to 6 people.
All you need is 4 pieces of wood 4 feet long and 15 inches wide to form the square. Then hinge a top made of wood strips with a plastic or glass cover.
How deep you set your cold frame into the ground depends on the local weather. You might want to consider sloping the sides when you construct the cold frame so that when placed facing south, it will absorb the needed heat from the sun.
Generally, the sun will keep the surface inside of the cold frame around 75 degrees, even on cool spring days. Now, if it gets too hot, just prop up the cover.
Don't pass up considering the use of a cold frame in your garden this year.