Build a Greenhouse for Early Spring Planting

With spring just around the corner, many homeowners have gardening on their minds. The seed catalogues are well worn from repeated flipping of pages. Seeds have been ordered, and some early bedding plants have been started. Many of us are itching to get outside and start seeding the garden, but it is too early. The days are warming but the nights remain too cold to allow seedlings to survive.

One way out of this dilemma is to build your own portable greenhouse. Designed by Agriculture Canada, the greenhouse consists of polyethylene-covered wooden frames that are bolted together and assembled in the garden. The greenhouse can be easily dismantled and folded flat for storage. It can be built to any size specifications, depending on your needs.

The floorless greenhouse allows light and heat to enter but prevents some of the heat from escaping. Thus, the temperature inside the greenhouse increases during the day. The soil over which the greenhouse is placed stores some of this heat. During the night, when the outside temperature is cold, the heat gradually escapes from the soil but the greenhouse holds enough of this heat to prevent frost from damaging the plants inside.

The system works well if the air temperature is not too cold, though additional frost protection can be achieved by using internal and external curtains.

The greenhouse can be set over the garden area in the early spring (March). For best results, the garden should be located in an area that receives full sunlight. As the air temperature builds up inside, any snow covering will melt and the ground will begin to warm. By mid to late March it is often possible to seed directly into the soil "floor" of the greenhouse. Only plants that tolerate a cool growing season can be seeded early. Warm-season crops such as such as tomatoes, peppers, cucumbers, require much more warmth that this greenhouse can provide.

As the days become warmer, too much heat may build up inside the greenhouse. It is very important not to let this happen, or you might lose your crop. The simplest solution is to leave the greenhouse door partly open to provide ventilation. When the days become quite hot, remove the greenhouse. In September it can be taken out again and placed over the garden patch to extend the growing season.

Adopted from an article by Grant Wood - University of Saskatchewan.