If you want to keep your greenhouse at the ideal temperature for overwintering most frost sensitive plants, a minimum temperature of 7C (45F), you need to heat it during the coldest part of the year (autumn and winter). Many gardeners never heat their greenhouse, citing ecological and environmental reasons for their choice. But if you donít heat it at all and rely on the heat of the sun to warm the glass, your greenhouse will only protect your plants from the weather such as wind and rain and will not necessarily protect anything that is not hardy.
To heat a greenhouse you need fuel or electricity. If your glasshouse has no power supply then you will need to rely on paraffin, oil or gas heaters. These types of heaters must be checked regularly to ensure that they have not run out of fuel and are burning evenly. Electrical heaters are much cleaner and fume free to use and can be fitted to a timer and a thermostat to ensure that the minimum amount of energy is used. Set the timer to control when the heater operates and set the thermostat to operate the heater when the temperature drops to a particular level.
The latest electric Energy Efficient Heater is a clever design that takes in the warmer air at the top of the greenhouse roof and then heats it up some more until it is at the right temperature and then recycles it back out into the lower realms of the greenhouse. To get the best out of it you need to position the heater fairly high in the greenhouse and then move the flexible outlet pipes so that the airflow is used to the best advantage. Itís on a thermostat so you can use it as a frost control to whir into action when the temperature falls below the level that you set. Whatís more you can even use it in the summer to improve the airflow within your greenhouse by switching off the heating element and use the fan to move the air around instead. Itís the ideal choice for a greenhouse up to 10x12 ft in size.
For a 10x8 greenhouse opt for the stainless steel Bio Green Phoenix heater. It is powerful and quiet and can be used to heat your greenhouse to suit the needs of a wide range of different plant groups. It comes fitted with a thermostat and three power output options, so you can keep your Growhouse at just the right temperature effortlessly.
If you only have a small greenhouse then you donít need a big heater. Instead opt for a small electric heater, thatís designed for 6x6 or 8x6 greenhouses. Choose a heater that is thermostatically controllable so that you can set it to come on when the greenhouse air temperature drops below your danger level. Most electric heaters can also be used as a fan without the heating function to circulate the greenhouse air around inside; this is an ideal extra function in the summer, when hot still air can simply linger in the glasshouse. Remember that good greenhouse ventilation is essential throughout the year.
Donít forget that for electrical heaters, it is vital to have an insulated electrical supply installed by a properly qualified electrician. The heater should not be plugged in to an extension lead, but instead plugged directly into a dedicated socket suitable for greenhouse use. Always make sure your greenhouse heater is kept well away from water and also any flammable materials and ensure that all your precious greenhouse plants are well away from the heater outlet or they may be damaged by the hot air.