Greenhouse insulation

Steve and Val Bradley explain how to protect your greenhouse plants this winter

- Steve and Val Bradley

HEATING a greenhouse, or even just keeping it frost-free, can be costly and with energy prices on the rise it makes sense to try to keep the price under control. Electricity, gas or paraffin can all be used effectively to keep out the cold and protect your tender plants, but make a good start by ensuring your greenhouse is as airtight as possible, mending damaged cladding (including mending or replacing cracked or broken glass) and making sure vents and doors are seated properly so they will fit tightly when closed.

Greenhouse fumigant

An easy way to check for any places where warm air could escape is to use a greenhouse fumigant when you are cleaning out your greenhouse in late autumn or early winter. Watch from outside and make a note of any places where the smoke escapes.

Probably the most commonly used material for insulating a greenhouse is polythene, either as clear sheets or bubble plastic. Whichever you choose, the most important thing is to make sure there is a gap between the cladding and the insulation, to help to create a temperature differential between the inside and outside of the greenhouse.

Plan which parts of the greenhouse need to be insulated, as it may not be necessary to cover everywhere. Unless very tall plants are being housed inside overwinter, it is a waste of plastic and heat to insulate up into the ridge in the greenhouse. The warmest point in any greenhouse is the highest part, so it is only really necessary to insulate to a point just above the level of the doors.