How To Heat Your Greenhouse
Tuesday, 16 February 2021 | Matt
It is becoming more and more important to learn how to heat a greenhouse efficiently because fuel is pricey and gardening without causing harm to the environment is one way people can give back to mother nature. Keep reading for some great advice on how to heat your greenhouse with minimal energy usage.
Electric vs Gas
If your goal is to save money you are better off to heat your greenhouse with electricity rather than gas. The need for ventilation when burning gas reduces the savings you may have had from burning it. Furthermore, a gas heater is only useful for those plants that thrive in lower temperatures. Electricity is more easily controlled and safer to use in a greenhouse.
There are some good possibilities of more environmentally friendly choices in the future such as ground source heat pumps but for now, they are not practical for use in a privately owned greenhouse.
Heat Sinks/Thermal Mass
If you have a smaller greenhouse it may be possible to create a no-cost heating option by building a heat sink. A heat sink absorbs the heat from the sun during the day and releases it at night or when it cools down. There are a couple of different options that will work well as a heat sink.
Plastic bottles are great simple and low-cost heat sinks. Begin by painting several plastic bottles black. Fill them with water and place them all around your greenhouse. The bottles will absorb the heat from the sun during the day. In the evening they will release the heat into your greenhouse. It may not seem like much, but it can make a big difference to your plants.
A second option is to build a thermal mass floor. You can do this by putting concrete slabs down on the floor of your greenhouse. The concrete acts as a heat sink because it is a material that will absorb the heat when it is hot out and release it as it cools down. if you opt for a concrete slab floor, it will act as a heat sink too. Some people choose not to pave the inside of their greenhouse, and that’s fine - but remember that having some concrete slabs will help you control the environment more. And while everything runs free and wild outside - a greenhouse is a controlled environment by definition!
How to Insulate Your Greenhouse Effectively
You will usually lose heat from your greenhouse because of draughts and building structure. Use the following tips and ideas to improve the heat holding capacity in your greenhouse.
If you choose to increase the temperature in your greenhouse using containers of water to give off warmth be aware that if the water freezes your plants will already be irreparably damaged.
During the winter there is little to be done about dampness and the resulting moulds and rots. Be sure to avoid dampness by ventilating on sunny days and using heat to dry out your greenhouse if you need to. It is better to spend a little bit extra on heat than lose your plants.
There are certain plants that need a high-intensity light. Insulating your greenhouse too much by adding a sheet of plastic or double glazing will cause these plants damage. Do your research before planting if your greenhouse is highly insulated. Winter lettuce and alpines are two crops that will not do well in a well-insulated greenhouse without grow lights.
On the other hand, there are plants that need little light but must never be allowed to freeze. In this case, an extra layer of insulation is well worth it. If you want to grow both types of plants it may be practical to consider a compromise, such as installing an extra layer of bubble polythene to the north-facing wall only, allowing the full light intensity to shine through in the rest of the greenhouse.
You can also learn how to heat your greenhouse without electricity here.