Guide written by:
John, Passionate gardener, Cambridge
Most greenhouses owned by home gardeners are not heated. However, in cloudy weather, these structures will only allow you to increase the temperature by a few degrees. If you want to generate more heat – for early seedlings, tropical plants or simply for very cold conditions – you will have to heat your greenhouse.
- Electric heating
- Oil heating
Insulating a garden greenhouse
Heating is only a cost-effective option for well-insulated greenhouses.
Even if your garden greenhouse is made of an insulating material – such as double walled polycarbonate sheets or double pane glass – it is still possible to increase the temperature by a few degrees by lining the interior walls (and the roof!) with bubble wrap. This can be attached to the frames using special clips.
Triple layer bubble insulation has significantly higher insulating power than low-end alternatives, and is also much more resistant.
Not all plants have the same temperature requirements. Keen gardeners sometimes set up two small greenhouses instead of one: an unheated greenhouse, with little or no heating for plants that are less sensitive to the cold, and a heated greenhouse, kept at a much higher temperature (around 10°C or even 15°C).
The two main types of heating: oil and electric
Generally used to heat small greenhouses up to 5 metres and so-called cold greenhouses.
This type of heating primarily serves to keep frost away and maintain a minimum temperature overnight or during extremely cold conditions.
Be sure to only use low-sulphur paraffin (also known as kerosene) as other fuels may produce gas emissions that are toxic to plants.
There are various types of electric heaters specially designed for greenhouses: infrared radiators, fan heaters, tubular heaters, and so on.
Opt for systems that circulate the air. These heaters produce a more even temperature throughout your greenhouse, preventing the outbreak of disease in any nooks and crannies. These systems can also be used with the heating switched off to ventilate the space during the summer months.
For a small greenhouse measuring just a few square metres, a small electric heater may suffice.
Comparing the two heating systems
Easy to set up and move
Economical to operate
Gets rid of water vapour (which promotes disease)
Low operating life (additional oil needed for back up)
No temperature setting
Requires frequent ventilation
Constant temperature via thermostat
Uniform temperature from floor to ceiling
Easy to move
No gas or smoke emitted
Fan function (no heating) in summer
Effective for large greenhouses (larger than 20 m2)
Requires nearby electrical supply
Cost of electrical energy
Dries out air in the greenhouse
Requires back-up heating system in the event of electrical failure
Whatever you choose, make sure to only use equipment intended for this purpose.
Don't forget to air out your greenhouse on a regular basis. It is a good idea to do this when the weather is warm. Correct ventilation will prevent the development of diseases that can spread in closely confined spaces.
Other greenhouse heating systems
Gas heating is a cost-effective option. However, it is difficult to regulate the temperature with this type of appliance, so the greenhouse must be carefully monitored. In addition, gas can emit fumes that are toxic to plants and humans – especially if not regulated correctly.
As with oil heating, gas heaters emit water vapour.
Propane gas cylinders are the most commonly used as butane freezes as soon as temperatures drop to 0°C.
A old makeshift method involves placing basins of hot water in greenhouses. This method can still be used as a temporary solution (to deal with excessively low nighttime temperatures, for example) as those extra few degrees can make the world of difference.
A heated mini greenhouse for early planting
When preparing early seedlings or making delicate cuttings, you don't require a lot of space.
A heated mini greenhouse will provide more than enough room. This system consists of a covered tray that is heated from the bottom by a heating element. You can easily make your own using a polystyrene fish box with a terrarium heating cable placed between two layers of sand at the bottom of the box.
Guide written by:
John, Passionate gardener, Cambridge, 61 guides
When I was young, I was already working in the family garden. Perhaps that is where my interest in plants and gardening came from. So, it was logical for me to study both plant biology and agronomy. At the request of various publishers I have, over twenty-five years, written many books on the subject of plants and mushrooms (a subject that is close to my heart).They were mostly identification guides at first, but shortly after they were about gardening, thus renewing the first passion of my childhood. I have also regularly collaborated with several magazines specializing in the field of gardening or more generally in nature. There is no gardener without a garden, I have cultivated mine in a small corner of Cambridge for the last thirty years and this is where I put into practice the methods of cultivation that will I advise you in as well.