Polytunnel Choices

[Geoff]

Doing a bit of searching it seems a while since polytunnels were discussed. After this poor Summer I am wondering if putting a tunnel over one of my beds would be sensible. It may be a bit of an indulgence as I already have two greenhouses. It probably wouldn't have a big payback, but when you add in travelling purchasing fresh is expensive, but it would keep me occupied on bad days. Thinking about it raises a few questions.

First is - how well do they work?
There are lots of you out there that use them so in a season like this how much of a benefit were they. My Tomatoes in greenhouses were way down on normal presumably caused by lack of light and temperature so I can't see a tunnel giving much advantage there. With the extra covered growing space more things could move inside so did other crops prosper. I always grow a limited quantity of early Carrots, Cabbage and Cauliflower in a greenhouse and they did well this year (it was good weather then) so I could expand those.

Second is - Ventilation.
Often pick up comments about ventilation being an issue. In a damp cool Summer how do you balance keeping fungal problems at bay with keeping the temperature up. Is a door or mesh at each end enough when the weather is good, my maximum size will be 12' x 30'. This is really part of the next question but I thought it was important enough to look at separately.

Third is - Design Choices.
There are many designs and suppliers out there which I think could be divided into a few classes.
The Posh - Haygrove, Keder and Solar. These carry a premium over the rest, how much extra do they offer. Mostly they look better and have specialist covers. Haygrove have sophisticated ventilation and a partially upright design. Keder have their unique cover, nothing special in ventilation and are a bit sloping in the smaller sizes. Solar again have a unique cover, good upright design but nothing special for ventilation.
The Basics - lots of suppliers that you would have to write a big comparison chart for. I think finding the most upright sides might be the deciding factor here, the Citadel Space Saver looks interesting.
Intermediates - there are some designs that add in curtained side ventilation (I have discounted permanent side ventilation) which goes back to question 2.
Cover Fixing. Can be buried - I don't really fancy that with the position I am planning. Wooden Base Rails - how easy are these, do you get tears from where the screws go through. Aluminium Clamping Systems - such as Northern Polytunnels, are they worth the extra.
Strength - they all claim to be strong, do you really need to go for the thickest tubes, does lack of joints make a difference.
Path - slightly odd question. Do you use the central height with either an offset path or one each side or put a path down the middle.

Fourth is - Supplier Choice.
Although design choice might also select supplier as I am likely to come down to the cheaper options I would be interested in some sort of supplier rating. I guess most have only bought once but might know people who have used other suppliers.

Bit of a long post but I hope it generates some discussion.

[JohnN]

Hi Geoff
You must have been reading my mind! I was about to post a very similar query, so I'm also keen to reap the benefit of our wonderful expert's opinions. (There, that should get 'em!)

[Gerry]

Hi Geoff and John,
My experiences are as follows.

Nine years ago a friend was looking for a tunnel and I googled "Tunnels for windy sites" as it would be on the Atlantic shore. An answer came from the Outer Hebrides saying most people there got them from Northern Polytunnels. This is where we got it from. It is still standing and the cover has lasted.

Three years later I bought a 36' X 12' from the same supplier and am delighted with it. However I devised my own ventilation system. The top half of the double doors at each end is mesh (scaffold protection mesh) with a polly cover on the outside which I can unscrew from the top and drop down and re-screw when extra ventilation is necessary.
I also fitted double thickness of mesh for the bottom 2' 6" on both sides and having bought the full cover it allowed enough spare to make curtains for the sides too. I know you have discounted this but it turned out quite simple to do with lengths of 4" X 2" pressure treated timber fastened with U bolts to the metal uprights. If you want I can send you full details with diagrams.

Path wise I have a centre bed and two paths which works quite well.

The sides being straight for about 3' is a great benefit.

Growing this year has been a struggle, tomatoes not ripening, but no more so than in my greenhouse. Parsnips, leeks, calabrese, carrots, cabbage, shallots, cucumber, beetroot etc have all done quite well in the tunnel. So much so that I fantasise about my whole veg plot being covered like this.

Hope this is of some help.
Regards, Gerry.

[alan refail]

Morning Geoff and John

I won't/can't answer all the points, but here are a few thoughts from my experience.

I put up a 35'x12' tunnel in early 2004. Like Gerry I bought from Northern Polytunnels and the cover is still in very good order, albeit a bit mucky on the northern side, but that doesn't lead to much loss of light.

As for benefits: I use it all year round - there is rarely any empty ground even in midwinter. As one crop comes out another goes in after the addition of a dressing of well rotted compost. It was not much benefit for tomatoes this summer - until the end of the season they were very slow indeed, though I now have boxes of trusses I picked green six weeks ago ripening/ripened up nicely. At the moment it has my October plantings of cabbages, kales, winter lettuces, chicories and endives, rocket, miner's lettuce, bunching onions, pak chois and oriental mustards, biennial herbs such as parsley and coriander, a permanent herb bed (around a granite boulder it was impossible to move when siting the tunnel) and a bed of strawberries. In the spring/summer it will have, in addition to tomatoes, cucumbers, a wide range of salad crops including heading and loose-leaf lettuce, small leaf salads, bunching onions, herbs, summer cabbage, climbing French beans, chilies and peppers. While it may seem a luxury to grow many of the above under cover, the advantages are many: my hens can't get at them and decimate them; no damage from winter snowfall; though it is as cold or colder on frosty nights there is less frost damage; very little or no problem with cabbage white caterpillars; watering may be a pain at times, but in a wet summer crops stay much cleaner than outside. And the main benefit: you extend the growing season at either end.

Some pictures from 31 May 2012 viewtopic.php?p=102814#p102814

As you can see from the pictures, I have a narrow central path giving 5' beds on either side.
As for ventilation I keep the doors open (doorway covered with Climbing Plant Support Mesh to keep the hens and ducks out!).

[Geoff]

Thanks for your replies.
Gerry : I hadn't discounted curtained ventilation only permanent ventilation like some firms offer.
Alan : I like the idea of pest free. I was thinking about fine mesh for the doorways when open, or even mesh doors with 'curtains' like Gerry. I also like the idea of lots of different crops as backups to outside and season extenders (or any season at all this year!).
The biggest problem I can see is that the bed I want to cover is the one in my North West corner as that would have least effect on other beds. In the photo it is the one with the salad cloche and carrot cage in June this year. The problem is it slopes quite a bit, the boards on the lower part of the windbreak fence are 6" and you can just about make out there are two steps of three boards each so 3' fall. I am thinking of a hollow concrete block wall with the foundation tubes concreted into them but it will be a lot of work and not that easy to get right. I haven't decided whether to try and fill it level (a lot of soil) or just have a lot of headroom.

[Colin Miles]

Hi Geoff - very interested in the questions that you raised and the answered received. Was seriously thinking about getting a tunnel last winter, but ended up getting and observatory instead. This summer has made wonder again. One problem is that there are only 2 of us though the idea of covering a lot of the plot appeals.

Alan - how did you get on in the very hot summers?

[Geoff]

He's probably forgotten!
I've emailed Northern Polytunnels with the photo for advice, might be interesting.

[Gerry]

Geoff,

Just a few points.
If you are not burying the polythene it is recommended that the tubes be concreted in.
First Tunnels have construction details and video on their web site.
The polythene is sandwiched between wooden battens and so doesn't tear, but ensure sharp edges are rounded off.
Attaching to wooden battens makes it easy to tension the polythene...you knock down the side rails before fully tightening the U bolts.
If you are fitting mesh to the bottom attach it to the top of the top rail with 2" x 1" batten before attaching polythene and leave the bottom of the mesh loose until the polythene cover is fully fitted.

It would all be a lot easier to explain with diagrams. If you want to PM me with your address I will gladly post some to you.

I would think that the best option for your site would be to level with blocks. They say a slope along the length is ok, but not across.

Regards, Gerry.

[Geoff]

Thanks again. I guess if I search their list of pdfs the details will be there, I'll see if they reply to the email first. We go over to the Colne area from time to time so I can pay their factory and display area a visit.

[alan refail]

Alan - how did you get on in the very hot summers?

He's probably forgotten!

Indeed! Though I'm not sure we've had one while the tunnel's been up

[Redfox]

I was also looking into a pollytunnel, but decided against it as I am planning on moving soon so it would be a bit silly to pay for it just yet. Will watch what others asy as I will get one when I move

[Colin Miles]

Hi Alan,

I went on the Northern Polytunnels web site and started to build. But when you get to whether to choose aluminimum doors or timber, double or single, which for the front and back and then the base, I don't really know which I could get away with - lot of money to spend for just the 2 of us even if it saves time and gives fresh veg. But their Garden polytunnel looks as though it could be a sensible compromise but wonder how long the timber would last here in wet Wales. I would reckon 10ft is the minimum sensible width. Also, the cover is not the anti-fogging or anti-droplet, but how good are those and how long do they work?

Comments welcome - as always!

[Geoff]

Not as much of a debate as I had hoped, our limited active membership these days mustn't be polytunnel users.
Gerry sent me some excellent information on how to start from a basic Northern Polytunnel and customise it. I was encouraged by the cover life reported by Gerry and Alan.
Spending many wet hours staring at the screen I have ended up going round in circles. I've also gone through KG back issues to 2004 and picked up a few more pointers to add to the indecisiveness (seems a while since there was a detailed article).
I've discounted what I called 'The Posh' suppliers in the original posting as I cannot justify the cost. I've also decided that width is everything and focussed my attention on 14'. Taking supplier advice on how to cope with a plot that slopes in both directions it seems that a longitudinal slope is not an issue but it is very desirable to level out widthways. Some suppliers have offered customised tubes to help this.
Looked at trenching vs. base rails and came down in favour of base rails (against the advice of at least one supplier) as it seems to me to offer the advantages of better tensioning for less work, easier replacement and easier to customise for my slope. Also I didn't like the idea of looking after the muddy strip on each side that trenching would create, easier to use concrete to send the water into the neighbours field!
Decided doors at each end will offer sufficient ventilation. I fancy sliding doors but am looking at DIY approach as not all suppliers offer it as an option. Anybody know a source of a simple sliding mechanism? I've read about lots of posh wardrobe kits but nothing basic.
The wife and I disagree about mesh over the doorways when they are open for ventilation. She favours nothing to increase ventilation and allow small birds in and out. I can't decide between anti-butterfly netting or something finer to deter carrot fly and aphids. The difficulty is how important are pollinators, anybody any thoughts? (question for the magazine?).
That got me to the big spreadsheet trying to compare six suppliers. I have realised I can easily visit three of them so that is the plan for later in the week. Combinations of overall height, vertical side height, tube diameter, hoop spacing, cost etc. make this pretty complicated. At the moment the favourites are a special offer 'Dream' tunnel from Premier and the 'Space Saver' from Citadel but neither of these offer a sliding door option. I shall visit First Tunnels and see if I can beat them down a bit so I can afford their sliding doors. Northern Polytunnels were too off-hand for my liking. Ferryman and Highland didn't seem to offer anything distinctive. Still open to feedback of others' experiences, I'll have to decide soon to get the out of season discounts.

[Colin Miles]

Hi Geoff. I'm still interested in what you have found and will find though not sure whether I can justify the expense.

[alan refail]

One thing I should have added: polytunnels can suffer from bird damage.

I have to protect against seagulls.

I posted a solution here viewtopic.php?p=55418#p55418