so - poly tunnels

[Mrs H]

This thread gives me polytunnel envy!! As a farm manager we always had polytunnels, huge ones and we grew so much in them however now bein a stay at home mum we just can't afford to put r own one in. R neighbour has one that he doesn't use anymore but he's not very friendly so I havnt had the courage to ask him!!
Good luck with the plans, u will love it if u get it. We raised all r seedlings in the glass house and then transplanted them to the pt. Worked a treat. Good luck. Xx

[grahamhobbs]

My experience is that greenhouses can get trashed by the wind very easily but not polytunnels. I've almost given up on our greenhouses, I inherited 4 small ones on our allotment, because each winter several panes in each would get smashed by the wind and glass is not cheap, especially if you think you will replace them with toughened(laminated) glass.
A fellow plot holder erected a largish greenhouse and within a fortnight every piece of glass was smashed by a wind. And we are in a relatively sheltered position in inner London.
Ok, her and our greenhouses were cheap aluminium ones - you can buy much better ones, toughened glass, rounded at the eaves, solid frames and gaskets, etc but they cost a lot more.
So yes the ideal is a small heated greenhouse, well constructed and carefully located, and big polytunnels (Thurston Green's advice regarding polytunnel details are spot on).
If you already have the walls of an outbuilding, you can quite cheaply convert this into a greehouse - I think Odsox did this.

[greenorelse]

Thanks very much for the advice. I think I've come down in favour of a polytunnel and we'll think about a greenhouse next year. We have a conservatory which we've used for starting things - I wanted to reclaim it for the summer, though! I can wait.

We can afford a decent big polytunnel, with crop bars etc. I'll have to think about buried plastic/battened down but I like the idea of not burying it.

Any more pointers, especially with regard to gales, which are nearly always from the south-west? I'll get those books shown earlier in the thread.

[Green Aura]

Ours isn't buried and I'm so glad we paid a little extra for that method. Our plastic is now almost defunct with a huge irreparable rip near the front.

On an old thread veggieman showed pictures of how his is built in Shetland so we're going to replace it with corrugated sheets like he has.

If we'd used the burying method we'd have had to dig it all back up - at least we only have to release the base bars!

[Odsox]

Any more pointers, especially with regard to gales, which are nearly always from the south-west?

We have two polytunnels and a largish greenhouse (and a small one) and wouldn't be without either if I could help it.
I think I must be the only one to appreciate that greenhouses and tunnels are completely different affairs and that they complement each other. For instance, tomatoes and peppers grow ok'ish in a polytunnel, but a greenhouse is much better for the job as they don't like the higher humidity in a tunnel but do like the higher heat of a greenhouse. Conversely lettuces, early peas, carrots and the like prefer the cooler conditions of the tunnel and would detest the high temperature/low humidity of a greenhouse.

Regarding gales, my tunnels are within 500m of the cliff edge and are bog standard with ordinary polythene and WITHOUT storm braces and have so far survived 100 mph + winds. The original one is 5 years old now and is end on to the south west, but I do have a screw eye on the windward end and during the winter months I have a rope guy securely fixed to a stake. When we get southerly gales it hardly notices, but gales side on makes the polythene balloon up rather alarmingly but even those have not caused any damage. My polythene is fitted by burying and is very secure ... I chose that method as it seems to me that fixing with batons along the side relies totally on the frame anchors when the wind blows, whereas burying it anchors it all round as well as the frame (belt and braces ).
Also burying the polythene stops weeds from creeping in from the outside, which is a big plus.

My greenhouse is actually sunk about 5 feet into the ground, which makes it very wind proof.
Pictures of it are here .. http://www.selfsufficientish.com/forum/ ... 38&t=18367

Hope that helps.

[oldjerry]

Completely agree,for me,always bury it,not least as its part of the construction process designed to ensure rigidity.Anyhow if it works for you,great stuff,but even in west cornwall (bloody incredible winter westerlies) the cover would do 5 yrs,not a big deal to dig up the cover that often is it?
By the way,if you think you can't afford a tunnel ,look around,when I'm on the train(once a week at present) I see loads of abandoned frames(and they're the pricey bits),remember they use the same as sheep shelters,so keep your eyes open.

[greenorelse]

Odsox, that is very impressive!

Which leads me to think...sensible people build houses with small windows on the north side and large on the south. But an east-west orientation PT (or 'normal' GH for that matter) has a huge north face which gets no sun but all the cold north winds.

Thoughts?

[Odsox]

I agree, my tunnels are more or less north/south, although I followed the stone wall line and so are slightly east of north to slightly west of south ... it was easier to type "south west".
They are also on a slight end to end slope, which makes a noticeable difference to the climate inside, the top end is always warmer by as much as 10 C on a sunny day even with both ends open.

The greenhouse is exactly south facing with the back wall insulated by my lean-to chicken house on the other side as well as being partly below ground level. This year is the first time the temperature inside has dipped below zero since I first built it 15 years ago.

[Green Aura]

The reason we didn't bury ours was because we knew that our skin would never last 5 years - all the locals are astounded we've managed to keep it through 2 winters this, it's third winter has finished it off. The base bars are very good, they keep it pretty tight, add to the overall stability and have made re tightening the skin possible (we were advised by someone we'd need to do this annually).

However, when we change it to the corrugated system burying the bottom pieces will make sense.

[oldjerry]

The reason we didn't bury ours was because we knew that our skin would never last 5 years - all the locals are astounded we've managed to keep it through 2 winters this, it's third winter has finished it off. The base bars are very good, they keep it pretty tight, add to the overall stability and have made re tightening the skin possible (we were advised by someone we'd need to do this annually).

However, when we change it to the corrugated system burying the bottom pieces will make sense.

Have you got no windbreaking then??

[Odsox]

..... have made re tightening the skin possible (we were advised by someone we'd need to do this annually).

Mine is easy to tighten as well Maggie, you just lift the hoops out of the ground tubes a little.
I did it after the first winter but haven't needed to since, I suppose it must stretch a bit but then no more.
My first one is 5 years old next March and the polythene is still sound but not so translucent, so I will probably replace it next winter/spring 2013

[red]

how long does the plastic last on polytunnels?

[red]

My experience is that greenhouses can get trashed by the wind very easily but not polytunnels. I've almost given up on our greenhouses, I inherited 4 small ones on our allotment, because each winter several panes in each would get smashed by the wind and glass is not cheap, especially if you think you will replace them with toughened(laminated) glass..

we had a problem with this, until we replaced some of the panes with outdoor perspex. its fairly cheap and definitely cheaper than replacing glass all the time.

one of our greenhouses is aluminium - we were given it for free. they often come up on freecycle if you are prepared to dismantle and fetch them yourself. to that end, there is always glass available too

[Odsox]

The problem with cheap aluminium greenhouses is the glass is thin 3mm and breaks very easy, even just with the flexing of the roof bars when you open the roof light.
My greenhouse because of the chance of strong winds down here, is made entirely out of 4mm standard window float glass and has survived many storms and heavy chicken landing on the roof.
It didn't fair too well with my grandson's catapult though.

I think 6 years is recommended by the suppliers for standard polythene, although you can buy (more expensive) longer life gauge.
I'm going to clean the cover of mine this spring as it's the first time it's been empty, and see what the transparency is like afterwards. If it cleans up nicely then I may leave it for 7 years as it's still pliable.

[Mrs H]

OMG I just had to come online and quickly tell u all!!! When I was out this morning I spotted a polytunnel frame in the middle of some scrub at the side of a house that is for sale. Some investigations later have revealed that the polytunnel belonged to a man who owned the property a few years back, the current owners bought the property with it in situ and hav let it disappear into the woodland. This afternoons task is to track down the current owner (the house is rented at the minute) and ask him if I can have it. Fingers crossed!!! Xx