Figure out your needs if adding greenhouse

Greenhouses are not magical. They attempt to re-create a suitable outdoor environment so plants can grow out of season. Providing that environment is sometimes more difficult than inexperienced gardeners realize.

Plants grown in a greenhouse need the same things outdoor plants need — warmth, light, water, mineral nutrition, air and space to grow.

Some of these are easy to provide in the greenhouse and cost you nothing. Others are expensive to provide, and the colder and darker it becomes in the winter, the harder it is to grow plants out of season.

First, consider warmth or temperature. With subfreezing temperatures, it is clear that temperature is a limiting factor right now. Want evidence? Look out your window and see what is growing in your garden. Everything is dormant, and other than hardy evergreens, nothing looks alive.

How warm does it need to be in a greenhouse for plants to grow? The temperature needs of different plants vary, but a convenient way is to divide plants into cool-season and warm-season crops. Warm-season vegetables include tomatoes, peppers, squash and melons, while cool-season vegetables include peas, lettuce, cabbages and radishes.

Flowers can be divided into similar groups. Some cool-season types are buried under the snow right now. These include pansies, wallflowers, foxgloves and many others that will survive nicely and bloom this spring. Warm-season flowers are those killed by the frost last fall, including petunias, fuchsias, impatiens and nicotiana.

The warmer you keep the greenhouse, the more fuel it uses and the more it costs. Keeping a greenhouse above freezing and growing cool-season vegetables and flowers is much less expensive than keeping it near 80 degrees and trying to grow tomatoes.

Light is the other expense. High-intensity lighting is expensive to buy and install, and it is even more expensive to operate. Since our days are so short and overcast right now, light is often the most limiting factor.

The cheapest and most effective way to deal with the limited light and low temperatures is to shut down the greenhouse or scale back what you are growing. The expense of trying to force the plants to grow is often not worth it when even Mother Nature isn't providing the basic needs of the plants.

In my own greenhouse, I'm not providing supplemental heat or artificial light, and it has been easy to see which plants are doing well and which are not.