Cold frames give gardeners a jump-start on planting

Cold frames give gardeners a jump-start on planting

As I am writing this, the ground is covered with snow. The most recent forecast I have heard indicates by the time this column is published, the temperatures will be nearing 60 degrees. This weather contrast certainly gets me into the mood for spring planting.

Normally gardeners do not even think about any spring planting in this area until after Valentine's Day. If you use some new products on the market, such as Greenhouse in a Bag, or follow the old tried-and-true technique of using a cold frame, you can get started on your spring garden during an early thaw in January.

First, let's discuss a cold frame. Normally a cold frame is a garden bed that has a frame of landscape timbers, 2-by-4s, or something similar surrounding the bed. On top of the frame is laid an old glass door or window frame. The glass frame is usually hinged on one side, so that the frame can be lifted out of the way when the gardener wants to get to the garden, or so that ventilation can be provided on sunny, warm early spring days.

Greenhouse effect

The cold frame works on a simple principle: When sun shines through a glass, the short rays of the sun can penetrate the glass. As the rays penetrate the glass, they lengthen. The longer rays cannot penetrate the glass pane and escape back into the atmosphere. Therefore, they are trapped under the glass. These trapped sunrays provide the energy that heats up the air below the glass. This process is known as the greenhouse effect.

The warm air then heats the soil adjacent to the air below the glass. Therefore the soil and air under the glass are warm enough for cool-season garden plants to grow, albeit slowly.

There is another natural heat source that can be used in conjunction with the greenhouse effect. Below the area of the cold frame, excavate about 2 feet of soil. In the excavated area, place a layer, 1 foot deep, of uncomposted manure. Then place a foot of topsoil over the manure. Use a good grade of topsoil. Don't buy the cheap, black soil found at many stores in the spring.

If you can't find a good grade of topsoil, make your own by adding peat moss to your existing soil in the ratio of two-thirds soil to one-third peat. Be sure you mix the soil with the peat really well.

As the manure begins to compost, heat develops. This heat is trapped under the cold frame, and keeps your young plants warm.

There are several variations of the above system that work nicely. You can substitute overwintering poly for the glass pane mentioned above. This plastic film was specifically designed for the greenhouse industry. The frame for the plastic can be nothing more than 2-by-4s.

You can also construct a free-standing structure that looks like a conventional greenhouse. You can either use galvanized pipe, wood or plastic pipe for the frame. Then you can cover the frame with overwintering greenhouse poly.

A new product to hit the market recently is called Greenhouse in a Bag. This product, made in Southern Illinois, is a small greenhouse that comes as a kit in a bag. Just take the kit out of the bag, assemble it within a few minutes, and you are ready to get your garden growing. Greenhouse in a Bag comes in various sizes, 2 feet by 4 feet; 3 feet by 3 feet; 3 feet by 6 feet, and 4 feet by 8 feet. All of these structures are 3 feet tall, have zippered sides and ends so that the gardener can easily get into the structure of plant cultivation and harvesting.

During the early spring sunny days, temperatures can reach above 100 degrees inside these cold frames. On those days, it is imperative that the gardener open up the cold frame for ventilation to occur. Otherwise tender plants can easily get too hot and burn from the heat.

Some of the plants that are traditionally grown under a cold frame are the cole crops, broccoli, cauliflower, cabbage, and lettuce, spinach and radishes. Dortha Strack even grows peas and turnips under a cold frame.

I do have a word of caution for you. Since the cold frame is usually covered, natural rainfall does not get to the soil under the frame. Therefore you must monitor soil moisture on a routine basis. You will have to provide water on an occasional basis.

If you are suffering from cabin fever and want to get an early start on your spring garden, whether it is vegetable plants or summer flowers, think about putting together a cold frame. You can be weeks ahead of your neighbors in producing those cool season vegetables, while you work away those winter blues.