A greenhouse can be invaluable in winter, keeping tender plants sheltered from the worst of the weather.
You can also use your greenhouse in winter for growing herbs, winter salads and citrus plants, plus sowing early seeds – discover seven projects for a winter greenhouse.
Insulating your greenhouse with a layer of bubble wrap will keep frost at bay while still letting in light. Find out how to do it, below.
Buy bubble polythene
Fitting panels of bubble-wrap into panes of a greenhouse
Bubble insulation wrap is sold on big rolls – usually 75cm wide – and is available in garden centres or online.
Create ‘double glazing’
Pinning overlapping layers of bubble-wrap to the wooden frame of a greenhouse
Cut the sheets to length but rather than trimming the width, tuck the excess polythene under as an extra layer. This keeps the polythene away from the glazing, trapping a layer of air between the glass and sheet to reduce heat loss – like double glazing.
Seal off draughts
Joining sheets of bubble-wrap with clear, weatherproof tape
Use clear weather proofing tape for gap-free joins between the insulation sheets. Fit the sheets carefully around vents to block out draughts. Plug gaps in glazing and replace seals around doors if necessary.
Create a curtain
Use bubble insulation as an internal curtain to divide your greenhouse up into smaller areas. Fix tightly around the roof and sides, down to floor level and anchor it down with something heavy. Once in place, you’ll find small areas often remain warm without heating.
Add heat only when needed
Turn heaters on when needed, off when not. An electric fan heater with a variable thermostat is a good option if you have an electricity supply. If you don’t, paraffin heaters are useful. Top up the fuel tank each evening.
Use a max-min thermometer
Use a max-min thermometer to check if heaters are working well. You could put a digital thermometer sensor in the greenhouse to transmit a reading to the display monitor in your home. Check regularly, especially in cold spells, to ensure the temperature remains above your desired level.
Other ways to grow plants in winter
If you only have a small number of plants to protect from frost, why not use a heated propagator, instead of insulating your greenhouse? Heating a greenhouse is expensive and may not be needed. Raise seedlings in an electric propagator or on a windowsill indoors, instead.