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Friday 1 November 2013

Keeping the greenhouse warm.

1st November and we have had a couple of cold nights on the row. Grass frost and thin ice on the water tubs.

The tender plants are in the greenhouse now, some will be allowed to go completely dry and dormant, like the dahlias, but a few will need to be kept in a frost free environment waiting for the warmer weather to return.

With the cost of heating bills very much in the news it makes sense to take various measures to reduce the costs.

The first thing I do is to reduce the internal volume that needs to be heated. As I am needing most of the staging my way of doing it is to reduce the height by creating a false ceiling with training wire and bubble wrap. It is always a relief when this is taken down in the spring (the training wires remain in place), but there is no point in heat going into the roof space. The walls of the greenhouse also get an internal skin of bubble wrap, not only does this cut down the draughts but it stops the heat going straight through the  cold glass. If you don't need all your greenhouse consider creating an internal division so that you are only heating a small area. Alternatively consider investing in one of those cheap, plastic-fabric freestanding 'greenhouses' which can be put inside the greenhouse, and then only heat that space.

The next thing is to group the plants that need protection. Try to raise them off the ground - cold air will sink and the ground will suck any heat out of the pots. On cool nights it may be enough just to put some fleece over them, but if the temperatures fall lower then you may want to ensure that any heater is placed close to those plants that really need the warmth, with the hardier ones on the edge of the heated area.

I use electricity to heat the greenhouse. I have a fan heater with various settings which I do not use all the time, and two tubular heaters which are suspended underneath the metal staging. These cost little to run and provide a gentle, non-drying background heat. They provide base heating for those plants on the top, which is perfect for propagating in the early spring, and also radiate heat to the plants on the lower shelf. On a cold night I can safely drape fleece over the benches and keep the heat in more efficiently. I do have a back up paraffin heater, but I am glad not to have had to use this as it requires frequent visits to the greenhouse during the night and is hard to regulate.

The greenhouse has a double door, and I can only insulate one side, but that is better than nothing. The main problem with all this internal insulation is that it restricts ventilation, on warm, sunny days I do try to open the door and ensure a change of air.

Of course all this only works if you do spend time checking on the plants and heating regularly. It does mean that you can't completely forget about gardening over the winter, but it won't be long before you will begin sowing seeds and a warm greenhouse will mean an early start.

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