For the greenhouse owner the winter can bring a variety of challenges, not least of which is the decision of whether to heat the greenhouse.
Generally this depends on the type of plants that reside within your winter greenhouse and what sort of winter gardening you wish to do.
Most greenhouse gardeners like to push the seasonal boundaries, after all that’s the whole point of having a greenhouse. It extends the growing season at both ends enabling the greenhouse gardener to start growing and cropping much earlier in the year and extending the harvest and sowing right into late autumn and sometimes early winter.
This year is a prime example as the mild October has enabled greenhouse growers to grow and establish more winter salads, herbs and winter crops with little if any additional heat.
Many greenhouse owners do not heat their greenhouse, instead relying on the solar energy harnessed by the greenhouse glass. However it is possible to heat a small area of a greenhouse without huge expenditure in terms of equipment and energy charges, even in a large greenhouse.
Think of a greenhouse heater as an insurance premium rather than a tax. If it saves you from buying new plants and allows you to grow a more prolific crop of flowers, fruit and vegetable then it offsets its purchase and running cost. Otherwise it simply adds to your energy bill, your carbon footprint and your conscience.
A simple thermostatically controlled electric propagator can provide a small area of warmth within a greenhouse. Position this within a tented, insulated area within the greenhouse and you will raise the internal temperature both within the propagator and in the growing space outside.
Consider the Jumbo Propagator offered by Gabriel Ash, which offers a very generous 2ft by 6ft (approx) of heated growing space. It’s an energy efficient way of protecting winter plants, enhancing rooting for cuttings and bringing on seeds and seedlings out of season.
Position on a raised growing bench and create an insulated growing tent of bubble wrap over and above to keep the warmth inside. Ensure that the plants are well ventilated on warmer days and keep a close watch out for any problems.
If you plan to heat your greenhouse over the winter months then ideally you need a mains electrical supply. You can heat a greenhouse using paraffin or propane gas, but an electrical heater is infinitely more controllable and barring a power cut should keep your greenhouse plants at the correct temperature.
Bearing in mind that greenhouses are almost always single glazed, to make the most of any energy expended on heating the greenhouse it’s a good idea to add an insulation layer to the inside of our glasshouse. You can create an internal ‘glazing layer’ of bubble wrap inside your greenhouse frame. Timber framed greenhouses are ideal for this as you can pin the bubble wrap onto the frame easily. Aluminium framed glasshouses will require special glazing clips.
When choosing a greenhouse heater consider the cost of running it against the value of your plants and any crops you plan to grow. Look out for energy efficient greenhouse heaters such as the Indiana offered by Gabriel Ash. (click here)
It’s a really clever design that draws warmer air from the top of the greenhouse and then tops up the temperature of that air, releasing it to the lower realms of the glasshouse where your plants are positioned. You can direct the warm air to any part of the greenhouse and because this heater is thermostatically controlled and utilises any warm air that has been heated by solar radiation, it requires less energy to operate. It can also be used to ventilate the greenhouse during the summer months.
For more conventional greenhouse owners, there are several fan heaters designed for greenhouse use. Choose the heater designed for your greenhouse size for optimum results and set the thermostat carefully so that your plants are kept at a temperature for overwintering that is not too warm to encourage premature growth, but is warm enough to prevent their demise.