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Greenhouse heating


by Adam Pasco

While I'm turning the heat down in my home to save energy and reduce CO2 emissions, here I am considering heating my greenhouse to protect plants and provide warmth for early sowings.


Adam Pasco at the entrance of his greenhouse on a snowy winter dayShould I feel guilty about heating my greenhouse? While I'm turning the heat down in my home to save energy, keep bills down, and reduce CO2 emissions, here I am considering heating my greenhouse to both protect plants through winter and provide warmth for early sowings. Of course I'll be keeping heat to a minimum, and insulating the greenhouse with bubble polythene to reduce heat loss, but my environmental conscience keeps asking me the same question.

Looking at things another way, I wonder if it's actually worth heating the greenhouse. Does the cost of heating exceed the value of the plants I'm trying to protect through winter? I'll need to do the sums and work out what the cost of replacing the plants would be. Some of them are quite special, like the melianthus I raised from seed, and quite large pots of agapanthus that I probably couldn't replace, and which would take an age to grow again.

A large electric propagator does provide an alternative for seed raising, just warming the area I need for seeds and seedlings rather than heating the whole greenhouse. The only problem is that I soon outgrow the propagator, forcing me to move seedlings onto the cooler bench alongside. What if the snow returns?

None of us wants to waste heat or money, and I'm certainly not the only gardener with an environmental conscience. Our hobby does require us to both protect tender plants and raise new crops from seed every year, so some heating is an essential requirement, isn't it? Or should I forget the tender stuff and concentrate on hardy plants instead? There's nothing wrong with parsnips, carrots and brassicas, but I am rather partial to tomatoes, cucumbers and aubergines. My dilemma continues…



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Gardeners' World Web User 25/01/2010 at 20:11

i've brought my frost fraring plats inside, turned down the radiator in hall and keep them there. my melianthus was plated outside last season and, although protesting a little, seems to fare well

Gardeners' World Web User 26/01/2010 at 00:24

I am sure there is a way a solar heating system* could be modified for a green house. The joy is they get hot inside the insulated tube even on cold days from solar radiation, the catch is it would need to be hooked up to some sort of a big heat sink under the greenhouse. (Added benefit of heating the soil at the roots.) They did a DIY version with hot air on "Its not easy being green", and on another show some people made a diy solar heating system form blackened copper pipes. Does anyone with experience of these technologies think it might work / be cost effective? I would love to know but wont be able to try it out myself for some years yet. *not photo elec pannels but the ones that heat a tube of water inside an insulated glass tube.

Gardeners' World Web User 26/01/2010 at 16:19

I grew tomatoes aubergines and peppers in an unheated greenhouse last year. I started them off in a propagator in the house, then onto a window sill and only outside when the weather had warmed up. A later crop but no problems with fretting over the heating/environment debate.

Gardeners' World Web User 26/01/2010 at 22:40

I find the big chunky candles from pound shops useful to keep an 8' x 6' greenhouse frost free .If you place one in a terracotta pot and invert another on top with a piece of broken crock over the drainage hole in the top pot.The broken crock still has to allow ventilation,but the heat generated will surprise you and chunky candles will last for several nights.

Gardeners' World Web User 27/01/2010 at 07:53

To reduce the cost of heating a greehouse it is necessary to reduce the area you are heating by using bubble wrap. The shelving area can be confined and a simple frame work erected to pin the b'wrap to. I use an elect. fan heater with thermostat and the cost is is kept to a bearable level.

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