Top ten tips for heating a greenhouse in winter
If you are feeling the chill then it’s time to turn up the heat...in your greenhouse! Greenhouse heating will protect your tender plants from becoming a frosted, soggy mush, and keep your young plants snug and warm until spring. Heating your greenhouse will open up a whole new world of winter gardening!
But heating a greenhouse can be an expensive luxury, and nobody likes the idea of wasting energy or money. So we’ve put together some top tips to help you keep costs down and make your greenhouse heating more efficient this winter.
- Insulate with bubble wrap - A layer of bubble wrap clipped to the inside of your greenhouse frame will reduce heat loss and block icy winter draughts. Even an unheated greenhouse will benefit from a layer of bubble wrap. Buy purpose made horticultural bubble wrap insulation from garden centres as this is toughened and UV stabilised. When buying greenhouse bubble wrap remember that larger bubbles will let in more light. You can also use greenhouse bubble insulation to wrap your outdoor pots, protecting rootballs from freezing weather, and preventing your favourite pots from cracking.
- Invest in a greenhouse heating system - Electric fan heaters are ideal if you have a mains power supply to your greenhouse. Fan heaters are particularly good for moving the air around the structure which helps to prevent cold spots and reduce the risk of disease. If you don’t have mains power in your greenhouse then a paraffin heater is a better option.
- Use the thermostat - Save money and energy by only heating greenhouses when necessary. Most electric greenhouse heaters come with a built in thermostat so you can set your greenhouse heater to only come on when the temperatures drop below a certain point.
- Choose the right temperature - Most plants don’t require tropical conditions so don’t waste energy and money on maintaining higher temperatures than your plants require. You can keep your heated greenhouse frost free with a minimum temperature of 2C (36F). Most tender plants such as pelargoniums, half hardy Fuchsias and citrus trees will be happy with a minimum temperature of 7C (45F). This is also a good temperature if you are protecting young plants and plug plants while growing them on. For really delicate species such as Sundaville and other conservatory plants you can increase the temperature to a minimum of 13C (55F).
- Use a thermometer - Invest in a good thermometer with maximum and minimum readings, and check it daily. By keeping an eye on the air temperature you will be able to use your greenhouse heater more efficiently and adjust it when necessary.
- Position heaters carefully - Electric fan heaters are best sited in an open, central spot at one end of the greenhouse. Always avoid positions where the heater is likely to come into contact with water. If necessary you may need to angle the greenhouse heater slightly to direct the airflow above plants that are stood close by. This will prevent their foliage being desiccated by the flow of warm air.
- Only heat the area that you need to - Heating a large greenhouse can be expensive and wasteful if you only have a few delicate plants. Group them together and erect a solid perspex partition or create curtains of bubble wrap insulation to divide the greenhouse into smaller areas which can be heated more economically.
- Use horticultural fleece - On extra cold nights a layer or two of horticultural fleece will provide several degrees more protection to your plants without the need to turn up the thermostat. Crops in greenhouse border soil can be protected by a handy fleece cloche. Remember to remove fleece during the day to ensure that plants receive adequate light and ventilation.
- Don’t forget to ventilate - One drawback of heating your greenhouse is the problem of increased humidity. Good ventilation is essential to prevent the spread fungal of diseases and maintain a healthy growing environment. You can prevent moisture from building up by watering plants sparingly, and early in the day. Clear condensation by opening greenhouse vents on warm sunny mornings. Close them again before the sun goes down to trap the daytime warmth in the greenhouse and keep it warmer for longer.
- Heated propagation - Invest in a heated propagator to help your seeds germinate. If you only make a few sowings then a windowsill propagator may be sufficient. Heated propagation mats are also useful for rooting cuttings and keeping your seedlings warm after germination. Turn your greenhouse staging into a handy heated bench.