Managing the climate of a greenhouse is about providing the plants with the right conditions for growth, flowering and fruiting. What you need to do will therefore depend on the kind of plants you are growing and the stage they have reached in their life cycle. Not all plants need exactly the same conditions so the kind of climate will depend on what you plan to grow in you greenhouse. Some will need high temperatures and high humidity in the greenhouse.

Others will require slightly cooler conditions in the greenhouse. It is often possible to reach a compromise and provide conditions that will suit most of your plants most of the time. You will not be able to provide optimum conditions for all the plants in your greenhouse. But by choosing plants that like similar conditions you will achieve acceptable results. For the amateur greenhouse grower some compromises are necessary. If you are growing commercially that is another matter.

A commercial greenhouse must provide an optimum climate for a specific type of plant. Otherwise you will lose money. An amateur who is dedicated to a particular species has to make some hard choices. It may be necessary to sacrifice variety for quality. If your greenhouse is devoted to orchids and only orchids you can provide the best climatic conditions. If you want to grow other types of plant you will just have to build another greenhouse.

For most gardeners such hard decisions are not necessary. It is possible to provide a climate that will suit many plants to some extent. You may also find that you can partition off part of the greenhouse to create a microclimate. Part of the greenhouse can then have a climate that is hotter or more humid than the rest. In a temperate part of the planet where there is a relatively long growing season it is often possible to have an unheated greenhouse.

An unheated greenhouse relies on the sun's rays and the residual heat stored in the ground to create a climate that is warmer than the outside environment. This is adequate for raising seeds and for growing vegetables such as tomatoes in the summer. Regulating the climate in an unheated greenhouse is mainly a matter of making sure that there is enough humidity to avoid pests such as white fly and red spider mite and enough ventilation to avoid mildew and botritus.

The lower the Temperature the lower the humidity should be. Air cannot hold much moisture at low temperature and rot will result if the greenhouse is not properly ventilated. Providing some heat will allow a longer growing season. If the greenhouse is heated in the winter it will be possible to provide a frost-free space for tender plants that live outdoors in the summer. A small amount of heat will provide a greenhouse climate in which some salads can be grown all fear round.

The simplest method of achieving a frost free greenhouse is the old fashioned one of placing a candle in a large plant pot with another one over the top. The plant pots heat up and continue to give out heat through the night. Your greenhouse will be frost free in several degrees of frost. If you intend to keep your greenhouse heated all day or if the climate in your region is very cold in winter you will need to invest in a more complex form of heating. Electric heating is by far the best option.

It can be thermostatically regulated to produce exactly the climate you need. Electric heating is expensive, but you can reduce heat loss by insulating your greenhouse with bubble wrap plastic. This is the same kind of material that is used in packaging. You can buy it in big sheets from garden suppliers. When it is clipped to the inside of the greenhouse it creates a double glazed environment. Insulating a greenhouse allows you to maintain higher temperatures in your greenhouse.

But you must be careful about humidity. Some ventilation will still be necessary. Venting the greenhouse in the middle of the day will control the internal climate. Cheaper forms of heating exist but any kind of combustion inevitably produces gases that are harmful to plants. They are best avoided. If you have plenty of wood then you might consider a wood burning stove. Rather than put such a stove directly in the greenhouse it would be better to use it as a central heating stove and pipe hot water through your greenhouse.

Gardening inside the greenhouse

A greenhouse represents a major investment for most gardeners. Even the smallest and simplest types of greenhouse do not come cheap these days. They also demand an investment of your time. So why should you consider a greenhouse. Perhaps the main advantage of a greenhouse is that is provides the gardener with a longer growing season.

This is particularly important in colder areas. A greenhouse will provide an early start for seedlings, warmer conditions for tender plants and a frost free environment for plants that will not survive out of doors. Another, less often recognized, advantage is that a greenhouse allows a gardener with mobility problems to garden at table height in warm conditions. Plants can be raised to a convenient height for the gardener in a greenhouse.

Simple staging, either homemade or bought for the purpose will create an environment in which a disabled gardener can enjoy all the pleasures of gardening without having to bend or stretch or get chilled. A greenhouse can become a favorite place to sit and enjoy the rest of your garden. On a cold winter day the greenhouse will keep the wind of and provide a sheltered spot to think about next year's plans.

What you use a greenhouse for will depend on your own personal preferences. Beautiful displays of alpines can be created in a greenhouse on benches covered with gravel. It may seem strange to grow plants that are essentially hardy in a greenhouse but it makes sense. Alpines hate to get wet. They are used to being frozen all winter but will not survive damp conditions. Their flowers are often small and can best be appreciated when placed on a bench.

Excerpted from the book Greenhouse Maintenance by Wings Of Success.

This excerpt has been edited and condensed for clarity.

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