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 greehouse. Some will need high temperatures and high humidity in the greenhouse. Others will require a 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 greehouse 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 re
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 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 bubblewrap 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 greehouse it would be better to use it as a central heating stove and pipe hot water through your greenhouse.
