heating a greenhouse (begod, it looks expensive).

torontoboy45

really am hoping someone can help me out here!

my new g/house is small, brick-built to a 1m height, with a capacity of 72 cubic feet.

I'm having some success in my first yr, with plenty of toms, capsicums, herbs, etc. and I've got some plans for winter-growing, but of course I need to make it frostfree. so I'm ordering the bubble-wrap. so far, so good.

the problem comes when I think about heating. some advertised paraffin heaters (for smaller g/houses like mine) come with a 4.5l capacity good for 80hrs of continuous burning. so if we experience a extremely cold few weeks in, say, february it looks like I'll be coughing up £10 p/week on paraffin, which doesn't resemble anything like money-saving!

or have I got this completely wrong?

any thoughts/suggestions most welcome!

alanobrien

As you have realised paraffin is expensive and i can guarentee the price will rise when winter comes. If you do want to go with paraffin, stock up asap as i have seen prices incorease easily 30% in the DIY sheds over winter. The problem with paraffin is it creates a wet heat which can in turn promote rot (without ventilation) which negates the point of heating a greenhouse :rolleyes: confusing isnt it ?

I grow a lot of exotics and have to store them over winter. I now use an electric fan heater with a thermostat set to just above freezing (circa 2c) this gives warmth and circulates air helping to avoid rot. Some people i know even use dehumidifiers but thats a seriously expensive step unless the whole greenhouse is sealed.

peter_the_piper

I think you'd be better off with a small propane heater with a thermostat, it shoild work out cheaper and more efficient. Lets just hope its not as cold next Feb as this one.

serena

You don't need to heat the air - plants don't walk around, so you can heat the base and keep their roots safe.So, look into having a heated sand bed, on which you can stand the plants, and cover them with layers of fleece in particularly cold spells.(I use the base of a large propagator which I have filled with sharp sand)

There's a very good description of using a greenhouse, and getting the best value from it, in Peter Thompson's book Creative Propagation (the earlier edition is better than the later one in my opinion!).He's particularly good on highlighting the costs that may be involved in keeping a few geraniums frostfree, when it would be more economic sense to ditch them and buy new in the spring. I also like the section on size of staging, and which pots to use for maximising your growing space.

As for growing overwinter, I have found that low light levels are more of a problem than temperature, with practically everything coming to a standstill in December and January. I do still grow salad leaves in a polystyrene fish box (ask the fish counter in supermarket), and also grow lots of early and hardy bulbs for a display in January when I really need it.

peter_the_piper

During last Febs cold spell I lost cuttings on a heated bench like this so be aware its not foolproof, what is? Also you need to keep a much closer watch on the watering as the compost dries out a lot quicker.

cjb02

serena wrote: »

There's a very good description of using a greenhouse, and getting the best value from it, in Peter Thompson's book Creative Propagation (the earlier edition is better than the later one in my opinion!).He's particularly good on highlighting the costs that may be involved in keeping a few geraniums frostfree,

Thanks Serena, just been on to Amazon and bought this book, looks quite good. also got another one of his called the self sustaining garden, which again looks interesting.

any one else interested, here is the book for 7p plus Amazon postage

http://www.amazon.co.uk/gp/offer-listing/0747032130/ref=dp_olp_used?ie=UTF8&qid=1251668702&sr=8-3&condition=used

goodwitch

I bought an electric fan heater for mine the first year and set it on a thermostat to just above freezing. My electric bill rocketed that year so I took the heater out and bought a plastic mini greenhouse for a fiver in the sale. I lined it with bubble wrap, put in a corner of my greenhouse and now grow my seedlings in that. If we have a really cold snap I double up on the bubble wrap. I've lost some seedlings but not enough to make me use the heater again.

Lotus-eater

goodwitch wrote: »

bought a plastic mini greenhouse for a fiver in the sale. I lined it with bubble wrap, put in a corner of my greenhouse and now grow my seedlings in that. If we have a really cold snap I double up on the bubble wrap. I've lost some seedlings but not enough to make me use the heater again.

I don't know where you live, but if I tried that here, I would end up with all dead seedlings, have you put a thermometer in there to see how low it gets?

goodwitch

I live in North Lincolnshire and our winters have been mild for the last few years. We had a bad one this year but I didn't put any seeds outside. I started them off in the house and left them in my spare room, in an unheated propagator I've just been given, until the worst of the weather had passed. I haven't tried a thermometer but it does sometimes go below freezing in the greenhouse. I have found it was the ones near the floor I was losing so now I put bubble wrap on the bottom shelf as well and cocoon the pots in it and have lost less this way.

a11waysindebt

I used a fan heater last year with a thermostat no problems auto on and off with a temp control built in.

I've just been given a superwarm 10 heater can't control the heat though.Thats all I know is that it gets very warm in there with it 27.9 last night with a minimum of 23.

Lotus-eater

goodwitch wrote: »

I live in North Lincolnshire and our winters have been mild for the last few years. We had a bad one this year but I didn't put any seeds outside. I started them off in the house and left them in my spare room, in an unheated propagator I've just been given, until the worst of the weather had passed. I haven't tried a thermometer but it does sometimes go below freezing in the greenhouse. I have found it was the ones near the floor I was losing so now I put bubble wrap on the bottom shelf as well and cocoon the pots in it and have lost less this way.

Oh right, so they don't go in there until the worst of the weather has passed, that makes more sense.
I know my tomatoes and chillies are ok in my unheated greenhouse until it gets down to about 2 degrees, I don't like leaving them in there under 5 or 6 degrees, but sometimes I have been caught out.
I sometimes lose one or two even at those temps.
This year I put mine in the border soil on the 1st of May and it was fine, last year I had a couple of nights in June under freezing and I was panicking running around with fleece and huge stones in the daytime to try to retain heat in there.
Because they were in the soil and not on racks probably I got away with it.
A min max thermometer is interesting because it enables you to see how cold it gets in your greenhouse and put that against the temperature forecast. You can then see with relative ease when you are going to have a really cold night, then I bring all my trays inside the house, nice and cosy. That way I get away without heating the greenhouse at all.
I did have a candle in a terracotta pot ready at the start of the year, when the toms were in the ground, but I didn't need it.