Many greenhouse owners will be starting to ask if they need to heat their greenhouse. Heating it helps protect plants from frost and allow vegetables, flowers and plants to continue growing during the colder months. However, it can be expensive and depends on the greenhouse and the plants grown.
For many gardeners the decision to heat a greenhouse or not does not have to be simply between heating all winter or not heating it at all. There are several ways of protecting plants from cold weather without constantly using a heater. Insulation, fleece, bubble wrap and careful choice of plants can all reduce the need for heating.
Pros of heating a greenhouse
Protects plants from frost
One of the biggest advantages is that heating it can protect plants from frost. Temperatures inside an unheated greenhouse can fall during a cold winter night. Frost can damage or kill plants that are not hardy enough to survive low temperatures. A greenhouse heater can keep the temperature above freezing, giving plants a much better chance of surviving the winter. This is particularly useful for young plants, seedlings and tender plants.
Allows plants to grow for longer
Heating can extend the growing season. Without heating, many plants stop growing when temperatures become too low. By keeping the greenhouse warmer, gardeners can continue growing certain vegetables and flowers during the winter. For example, some crops can be started earlier in spring if the greenhouse is kept warm enough.
Protects tender plants
Some plants are unable to survive cold British winters. Tropical and subtropical plants, certain flowers, citrus plants and other tender species may need additional warmth. Heating the greenhouse can provide a suitable environment for these plants. Instead of bringing plants indoors, a heated greenhouse can provide a separate protected space.
Useful for seedlings
Seedlings are particularly vulnerable to cold temperatures. A heated greenhouse can provide stable conditions for seeds to germinate and young plants to develop. Maintaining a suitable temperature can improve germination rates and reduce the risk of young plants being damaged by cold weather.
More control over growing conditions
Heating gives the gardener greater control over the greenhouse environment. Rather than relying entirely on outdoor weather conditions, the temperature can be monitored and maintained at a chosen level.
This can be particularly beneficial for gardeners who want to grow plants that would normally struggle in their climate.
Cons of heating a greenhouse
Increased energy costs
The biggest disadvantage of heating a greenhouse is the cost. Greenhouses lose heat quickly because they are designed to allow sunlight in, rather than retain heat like a house. During a cold night, a heater may need to work continuously to maintain the temperature. This can result in significant electricity or fuel costs, especially during long periods of freezing weather. For a small greenhouse, heating may cost more than the value of the plants being protected.
Environmental impact
Using electricity, gas or other fuels to heat a greenhouse can increase energy consumption and carbon emissions. This is an important consideration for gardeners who want to reduce their environmental impact. Heating a greenhouse that is poorly insulated can be particularly inefficient because much of the heat escapes through the glass or plastic.
Heating may not be necessary
Not every greenhouse needs to be heated. Many plants are naturally capable of surviving cold conditions, particularly hardy vegetables and perennial plants. Crops such as winter salads, some herbs and hardy vegetables can often tolerate low temperatures. If the greenhouse is only being used to protect hardy plants, heating may provide little benefit.
Risk of overheating
Although winter heating is intended to prevent temperatures from becoming too low, a greenhouse can sometimes become surprisingly warm during sunny winter days.
If a heater is poorly controlled, the temperature may rise too much. Good ventilation and a thermostat are therefore important when heating is used.
Equipment and maintenance
Heating a greenhouse requires suitable equipment. A gardener may need to purchase a heater, thermostat, cables and possibly insulation. There is also maintenance involved. Electrical equipment must be kept safe in a damp greenhouse, and fuel-burning heaters require proper ventilation to prevent dangerous gases from building up.
Alternatives to heating
Before deciding to install or use a heater, there are ways to reduce the effects of cold weather. One of the simplest is to use bubble wrap as greenhouse insulation. It can be attached to the inside of the greenhouse and helps reduce heat loss. Horticultural fleece can also be placed over vulnerable plants during particularly cold nights. Moving plants away from the edges of the greenhouse can help because the glass becomes very cold.
Using a greenhouse thermometer is also important. Rather than heating the greenhouse continuously, a gardener can monitor the temperature and only provide additional heat when frost is expected. A thermostat-controlled heater can automatically switch on when the temperature falls below a chosen level.
For most gardeners, the best approach is likely to be targeted heating rather than heating the greenhouse continuously. Using a thermometer and thermostat means heat can be provided only when temperatures become dangerously low. Combining limited heating with insulation can provide a good balance between protecting plants, controlling costs and reducing energy use.
If temperatures regularly fall below the safe level for the plants being grown, then heating would be worthwhile. If the plants are hardy enough to cope with winter temperatures, leaving the greenhouse unheated is likely to be the cheaper and more environmentally friendly choice.
