I've wondered about this for ages but never bothered to ask as it didn't apply to my previous grows. But now I've got a few girls just starting to flower in a polytinnel, it's time to ask.

I read on here a good while back (if I remember right) that the ideal temps are under 30c during the day, and above 19c at night, and that at 15c the plants metabolism slows and at 9c they die. Which is all fairly easy to achieve with indoor grows, but what happens when plants are flowering by thier own time clock (not forced), it's getting into autumn and the temps drop? I don't expect my girls to finish before late October at the earliest, although the info on them (Magic Bud) says mid October. By then the nights will be getting pretty cold. Added to that the need to keep the polytunnel vents open to to keep the humidity down, which will let let any warmth in the tunnel out and cold air in.

So, if the temps I quoted are right, how do the plants survive our autumns when grown outside? And for guerilla growers it must be worse, 'cos thier plants are completely at the mercy of the weather, but I know they do survive.

plants can survive outside even in uk up to november, even december. they're tough things. cold nights are good to speed up ripening and deepen colouring. i reckon it's pretty cold in the middle of the night in the foothills of the Himalayas! mould, not temperature, is our no 1 threat. well, that and old bill.

Keep the r/h down in your p/t by keeping doors/vents open 24/7 if possible. The better the air circulation/movement the less chance they will get bud rot. If the r/h is still to high after doing this you might need to place an oscillating fan in the p/t to keep the r/h in check.

Peace,
GG

Thanks to both of you. I'll keep everything open 24/7, and keep an eye on the RH. Do you reckon covering the ground (bare soil) with plastic sheeting to keep evaporation down, would help?

ETA - was gonna try to get some photos up today, but I've just not had time. Will try to do it before the W/E.

ETA2- So what was all that I read about them needing high temps? Does that just apply to indoor only strains?

I would not cover the bare ground with plastic as the soil will not be able to breath and could go stagnant, great conditions for fungal root infections. The Ideal temps are 70*f to 80*f lights on, knock 10/15*f for lights off but try not to let the temps fall to far below this, good r/h 75% for veg and r/h 45% during flower lights on, the r/h will rise a little during lights off but keep a small oscillating fan operating will sort that out as long as it's not to high.

Peace,
GG

Thanks GG, I didn't think about the ground not being able to breath. Sorry to be dense, but when you say use an ocillating fan, but not too high, do you mean high powered or too high off the ground? And, would an oil filled rad be OK to boost temps a bit at night? Sorry for so many questions.

Hiya Mygarden,
Don't put yourself down Mygarden, we all started some where and you will soon learn if you want to grow good bud.

An oscillating fan is a motorised fan that goes side to side automatically, and you want the fan to be blowing left to right, right to left across the top of the canopy and as the canopy get taller you raise the oscillating fan to keep the air blowing across the top of the canopy. This will help keep the air circulating at all times which makes it harder for bud rot spores to get a foothold on the plants service, it will also help keep the r/h down. An oil radiator will help if the temps are really that low in your greenhouse, but do not keep it close to any plants, canna plants hate constant dry heat and there leaves burn easily.

e2a: A 16 inch oscillating fan with 3 speed settings and height adjustment will be perfect for the average sized greenhouse.

Peace,
GG

Thanks GG - I do have a fan, but it's a desk model, and too powerfull for the plants, even on the lowest setting. So I'll google one and see if there are any going cheap at this time of year.

Hot dry conditions are great for Spider mite too!

Now my plants are in the ground, how do I go about feeding them? I mean, they will dry out slower than if they were still in pots. So how do I get enough feed into them without overwatering? Or will they need less now they have a bigger root run? But then again, will the new compost have enough potassium in it for flowering? Questions, questions...

I am growing in a polytunnel too and I keep the door open but covered with shelter shade netting 24/7 and I leave an oscillating fan running in front of the netting to draw air in.

Since doing this I have noticed no condensation gathering on the inside of the polythene.

When the colder nights draw in I will be heating the p/t and closing the door but I have given my girls a good spray of Dithane which is a long lasting preventative fungicide. I am hoping this will give me a better chance of avoiding budrot. If you fancy using any its available in most garden centers but I would do it quickly as you dont want to be spraying anything too late into flowering.

Good luck with your grow.

Mr. W

Hiya Mr W,

I’m using a poly tunnel and used a twin paraffin heater/burner on full 24/7, £11 a week in paraffin and it did not raise the temps at all when the temps dropped, so I thought I better do some research and every thing I have read say's that it is quite difficult to heat a poly tunnel because it's plastic and does not hold heat hardly at all, so the consensus seems to be, if heating a poly tunnel it is going to cost a lot of electric/paraffin/money to keep it heated and would have to be on 24/7 to keep the temp constant because plastic holds heat so poorly.

But if you do heat your poly tunnel I would Mr W I appreciate it if you could let me know what you think or has heating a poly tunnel worked satisfactorily for you before through previous winters? What are you going to use as a heat source?

The only suggestion that came up instead of using a heater was to use heating cables in the soil or trays. Yes I wanted to keep the roots warm but I also wanted to keep the circulating air warmish too, so I decided not to go with heating cables. Plus heating cables are quite expensive to buy and probably expensive to run.

Peace,
GG

Insulate with bubblewrap to keep heat in, keeps wandering eyes out too!

I use an electric 2kw greenhouse heater which blows the warm air across the plants.

I will just position my heater in such a way that it keeps a constant flow of warm air passing through the plants and keep the door closed so the heat isn't completely wasted

Hiya Mr W,

Having a heater blow hot/warm air throughout the actual plants will/can cause wind burn to the leaves surface I have read and this is why professional greenhouses are fitted with hot water/oil pipes the length of the greenhouse so the heat can radiate out rather than being blown out as dry air and drying the surface of the leaves quicker than the leaves can create moister which can cause wind burn. Have any of your plants shown evidence of wind burn or do you have plenty of room in your p/t.
Is your heater expensive to run because most electric heaters eat electric I have found?

Mygarden an oscillating desk fan will do until you can get a standing one, surely it can't be that powerful if it's a desk fan, I have a 16 inch oscillating fan that is great on setting 1 and 2 clip on 6 inch fans in a space of 1mx2m indoors. The fan needs to be powerful enough to gently move the plants side to side to strengthen there stems, you trying to create a gentle breeze in the p/t like outside when you see plants gently swaying in the breeze.

Peace,
GG

Hiya Rm,

Bubble wrap is good for insulating, but I thought it might trap all the condensation in between the plastic p/t wall and the bubble wrap and could then be a catalyst for bud rot spores if the moister cannot escape and conditions are favourable, have you tried it successfully yourself before.

Peace,
GG

Not tried myself but have seen alot of ghouses done up like this. I can see moisture getting trapped between the glass and wrap but if the interior is well vented then it should be nomore a problem than without?

I thought about insulating with bubble wrap, but wasn't sure how effective it would be. I can imagine that any form of heating is going to cost a bit, and I am really interested in any ideas anyone has about this. I will get hold of some dithane, as long as it's not one that's been discontinued due to the new EU regs. B&Q did a concentrate that I read was ace at dealing with spider mite, and could be used on edibles, but that's been done away with, and I didn't get some when it was available.

GG - I got a pedestal fan from comet for £11 - just the job. Though haven't needed to use it yet due to the gale force winds (almost) we've had the last few days. My desk one really is too powerful. I bought it in 1987, during that really hot summer and was royally ripped off, but it's lasted that long and blows a gale.

I'd like to post some photos of my grow, but to be honest I keep putting off, I'm a bit paranoid about putting photographic evidence on the web.

Hiya Rm,

I think it might work better if a gap of a couple of inches is kept in between the b/wrap and the glass/plastic, this way the condensation could be vented out through the windows. But to get rid of the condensation and keep the r/h down it will need a decent oscillating fan in there, especially when there is prolonged wet weather and the r/h outside is high.

Peace,
GG

Hiya Mygarden,

I have not done a diary for the same reason if I want to be truthful, but I have posted a fair few pictures of my ladies and babies. There are members on here that have had diaries/photos on here since 2001 and nothing has ever happened to them.

I think the security is so good on here because the servers are in Amsterdam and so our own police cannot get to the servers with all our details in, which are probably incripted any way Mygarden, honestly, I wouldn't worry to much about it we have over 50,000 members now and it rises daily, but if your going to loose sleep with paranoia then probably not a good idea, as long as your not in the picture who can prove any thing anyway.
e2a: A large oscillating fan for £11 is a very good deal, probably because of the rubbish summer we have had yet again.
Peace,
GG

GG - I didn't realise the servers are in Holland - very smart. OK, you have put my mind at rest so I will do my best to get some photos taken, but I won't do a diary. Wow, so many members, just shows how wrong the law is.

Hiya Mygarden,

Yes, the law is wrong concerning cannabis for adult recreational/medi use and the number of members on UK420 a lone is comforting. From what I have read and been told, uk420 is by the safest place to be because the servers are in Amsterdam, so if I was to upload pictures to any canna forum, it would be this one, which I've already done quite a few times.

Take care,
GG