greenhouse heating

[Billy's lad]

I am a very novice gardener so please bear with me

After a really sharp frost the other night it has got me thinking about heating the greenhouse

I am thinking about under floor heating via a homemade solar panel

The solar panel is a radiator in a large wooden box with an old shower door on the front and pumped round with an old central heating pump

The Under floor heating will be installed the same as a domestic set up on insulation covered with a sand cement screed

I know it wont contribute a lot in the depth of winter or dark days but I have most of the stuff and thought it would help retain heat like a storage heater

[bramble]

Hi Billy.
I can't comment on the type of heating you are planning to put into your greenhouse as I wouldn't have that kind of know how...however I am wondering what it is you want to grow over the winter months. Be aware it's not just heat your plants need but light levels as well which is just as important.
I will be watching this thread with interest and good luck with your project.

[muck lover]

Well that might be something to bear in mind at some stage. However if you are a novice gardener I think you would benefit from learning to grow in your greenhouse and garden under normal climate without worrying about heating anything.
If you are technically minded - and you really sound highly technically minded- your efforts possibly would be better concentrated on heating a small propagation area for seed sowing, rigging up an automatic irrigation system for the greenhouse, maybe getting some growing lights going on a timer for early plant growth in spring and even getting an automatic ventilation system going for sunny days.
Heat without light isn’t very good for plants. Of course you may progress to growing tropical fruit and veg some day and in that case an underfloor heated growing area sounds fab.

[Billy's lad]

I have a load of ( 50 plus ) pelargonium cuttings and dont want to lose them but dont have enough windowsill space inside

Last year I also grew some rocket potatoes that started off in pots in the greenhouse that worked really well , I put a oil filled rad in there last year but it was expensive

I am a builder so know my way round UFH etc but not plants or greenhouses

[rary]

To me half the pleasure of gardening is trying out different things and I don't just mean plants, if you are providing bottom heat you should be able to keep most plants over the winter, even if the tops get frosted with a small bit of heat the roots should be ok, at present I have lettuce, radish, rocket and pea shoots growing in the greenhouse without heat or additional light,and I harvest some quite regularly, if you don't try you will never know

[Billy's lad]

Awesome advice Rary !

I will post some pics up with progress

[Jay-ell]

Bearing in mind that greenhouses aren't that well insulated if you are attempting to heat all the air then a lot of heat will be lost through the glass.

Looking at this calculator to heat an 8x10 greenhouse with an average height of 6 feet by one degree is 131 watts or 447 BTU an hour.

So if you wanted to heat it to 5 degrees and the outside temp is -2 your going to need 918 watts or 3132 BTU an hour - so overnight (lets say around 14 hours) is about 13kw or 45k BTU.

The average energy of the sun at the ground is around 1kW per square meter but varies with latitude and season and even commercial solar panels aren't that efficient so to get enough heat to last through the night is going to need a very large panel plus you are going to have to figure out how you are going to store the heat until the night.

Of course you could try to improve the insulation using bubble wrap which might knock it down but it's still going to be several kilowatts a night.

Of course, as Rary said, if you can keep the soil temperature up the air can still be colder so you might want to look at using the soil as a heat store rather than underfloor heating to heat the air. That way it'll protect the roots and gradually cool down over night.

Using fleece and cloches an then give extra protection and keep some of the heat nearer the soil level.

[Penellype]

I think you will struggle to create much heat at all in the winter. I have a 4kw solar panel array on my roof, and in December and January it struggles to produce 2kwh throughout the whole of a sunny day, and there are some days when it produces almost nothing at all. This is simply due to the short daylight hours and the angle of the sun at this time of the year.

Have you considered creating a hotbed in your greenhouse? I think this would create more actual heat than any sort of solar power in winter.

[4Shoes]

I expect you would get similar if not more heating by building a "hot bed in the greenhouse" Just need fresh muck to keep the heat up.

[rary]

After reading your first post again, and noting what materials you have you could always consider a two stage system where you could send all the heat to a soil bed or if weather is good circulate over the full floor area, one other thing I would like to mention, using a fan to circulate the air can prevent frost damage to even the tenderest of plants,I have avoided dahlias getting damaged by simply moving the air within the greenhouse, so with a wee fan and your heating system, the world's your occster

[Jay-ell]

I have avoided dahlias getting damaged by simply moving the air within the greenhouse, so with a wee fan and your heating system, the world's your occster

You may of course opt for a solar electric fan - the choice is yours.

[Billy's lad]

rary

Thanks for that It would seem to be some benefit in the spring but not hold off minus two and below

[nickdub]

This question really comes down to what plants you are considering the heat helping - what is a good idea for tomatoes say, is not necessary/desirable for other crops.

You mentioned pelargonium cuttings and ruled out the house because of limited windowsill space. While its true that these cuttings need reasonable light in the summer, in the winter you can let them go almost dormant and as long as they are dry and frost free they will mostly survive.

What I'd do is put the cuttings in the greenhouse now and let them dry right out ie no water - then in a month or so time bring them inside in a box or bag and store them over Winter in a corner of a room. In the Spring take them out to the GH again and water them thoroughly by standing in a tub for a day or so - about 90+% should survive.

[Billy's lad]

nickdub

so the pelargonium cuttings will be ok without as much light ?

I have space that they can come inside but no windowsill , some got touched by the minus six the other night and I was going to cut off the affected leaves and see what happens

it is these cuttings and some others that are most important , I also plan to start off some spuds in containers in Feb probably rocket

[nickdub]

Yep bring them inside - obviously a bit of daylight is good, but the main thing is no water - as long as they are dry they won't try to grow much at all and the risk of them rotting is reduced - obviously you're likely to lose a few, but that more or less goes for all plant growing - which is why getting plenty of spare cuttings started in good time is the best insurance.

I try to over winter mine in a cold greenhouse, which works some years and not other depending on the frosts - but I'm a bit on the lazy side and its not worth the hassle of arguing with my wife about bringing a few plants in to the house compared with buying a few replacements. :-)