Growing plants in a greenhouse is an excellent way to have fresh vegetables and flowers throughout the winter. Plants need relatively warm temperatures to grow, and heating a greenhouse all winter can be costly. Here are some tips to keep your greenhouse warm and lower your energy bills.
Clip a layer of bubble wrap to the inside of your greenhouse frame to reduce heat loss and block drafts. This can help even if your greenhouse is not heated. Use horticultural bubble wrap from a garden center because it is toughened and UV-stabilized. Larger bubbles will allow in more light. You can also wrap outdoor pots to protect plants from freezing and pots from cracking.
An electric fan heater can be helpful if you have a mains power supply. A fan heater can circulate air to prevent cold spots and reduce the chance of your plants getting diseases. Put an electric fan heater in an open, central area at one end of the greenhouse where it will not come into contact with water. You might need to angle it slightly to direct the airflow above nearby plants. If your greenhouse does not have mains power, try a paraffin heater.
You can save energy and money by only heating your greenhouse when necessary. Use a thermostat to make the heat come on only when the temperature drops below a certain point. You can avoid frost by keeping your greenhouse at least 36 degrees Fahrenheit. Some plants need higher temperatures.
Install a thermometer with minimum and maximum readings and check it every day to see how the temperature fluctuates. This will help you know when to adjust your heater.
If your greenhouse is not full of plants, you might not need to heat the whole thing. Group your plants together and put up a partition or curtain of bubble wrap to divide the greenhouse into smaller areas that are easier to heat.
On very cold nights, use a layer or two of horticultural fleece to protect your plants without having to turn up the heat. You can protect plants in border soil with a fleece cloche. Remove it during the day so the plants can get enough light and ventilation.
Heating a greenhouse can increase humidity. Ventilation can prevent fungal diseases and create a healthy environment. Water plants sparingly in the morning. Open vents on warm, sunny mornings to clear condensation and close them before the sun sets to trap heat in the greenhouse.
Use a heated propagator to help seeds germinate. If you only sow a few plants, a windowsill propagator might be enough. Use heated propagation mats for rooting cuttings and keeping seeds warm after they germinate.