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Polytunnel Regained


Finally the weather has changed and Wednesday was a calm, warm and sunny day.
A few rapid phone calls and we managed to assemble six good friends to help us cover the tunnel, recently stripped of its cover in the big storm.
Determined not to have it fall over at the next gale, I’d already spent several days building sturdy doors out of polycarbonate sheets and timber frames. I also took the opportunity to put some vents in over the doors also made from polycarbonate. The door sills are of heavy timber and the posts placed in metal shoes which are bolted to the sills. A very sturdy structure.
As the tunnel is constructed on ground with a pronounced slope, it was always difficult to cover it well, and the first effort six years ago produced a sagging result. Every time it rained heavily rain would collect on the roof panels which would sag downwards like large balloons filled with water. Inevitably, the polythene tore in places and the pooled water used to drip through making the situation even worse.
Before getting the cover on this time, I was fairly sure we would never be able to get a good result, but with so many people helping this time it was easy. We hefted the heavy roll on to the central roof bar, then unrolled it down the length of the tunnel, pushing from underneath by standing on some steps.
Once the roll was at the end, it was possible to level it horizontally on the centre bar and then to pull down enough polythene at one end, while unrolling the roll further.
We could then unfold the polythene outwards and downwards and make sure there was adequate on both sides.
Rather than burying the edges in soil, which is very hard work and makes tensioning more difficult, this time I’d fastened boards to saddle clamps all around the base.
With three people tugging the polythene outwards at either end, and two of us pulling the polythene down, we managed to clamp the polythene between the base planks and start screwing them together, starting in the middle. We repeated the process on the other side, and then worked back and forth, tensioning as we went.
By the time we got to pleating and fastening the ends, with all hands still tugging and pulling, we found we had a beautiful polytunnel with the polythene stretched like a drum over its whole length. No more worrying in heavy rain!
The real solution to successful polytunnel covering is clearly to have as many helpers as possible. I’d guess you need six as a minimum, two at each end pulling at the bottom and top, and two in the middle tensioning and screwing the polythene between the fixing boards.
Now at last I can start sowing seeds, getting the peas and beans planted inside, with early carrots, Chinese greens, radish and salad, as well as starting off plants for the vegetable garden.

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You obviously knew exactly what you were doing Bertie, and it will defy the weather in future. I really envy you all that covered warm space, even on a dull cool day it will be nice to garden in there. I like your idea of screwing two planks together to hold down the sides, presumably you'll stake them down.

18 Mar, 2010


Hi Heron,
The planks are screwed on to the metal frame with saddle clamps so they are held really firmly. I didn't know about those when I first put the tunnel up.
You are right about how good it is to have a tunnel. I've missed having somewhere to go in all the cold weather recently but today it was bliss, though it's got very hot already. I've found by opening a vent at one end with a door open at the other, a blast of hot air comes rushing out.
The only design fault is that the doors need another bolt on the inside so you can keep them closed when working inside on a cold day.
Good gardening to you, and I hope spring has finally arrived back in the UK and you can make progress on the garden,

Best wishes,

18 Mar, 2010


Yes but what holds the frame down? As for the door, it sounds like a job for a boy scout with some string in his pocket. It sounds idyllic in there, warm and bright. I can understand how the hot air rushes out through the vent. Could you pipe it to your house to save on heating bills.

18 Mar, 2010


Not sure I know what you mean. The metal frame is held down really securely in base tubes which are concreted into the soil. The wooden frame door frame is attached to heavy timbers half buried in the soil. I'm going to put a couple of old concrete blocks in front to be doubly sure nothing moves.
Like your idea about heating the house! I was reading somewhere recently about someone who had built their polytunnel as an 'extension' so the kitchen door opened straight into it. Wish we could do that (not enough space there) though I don't think my wife would approve!

19 Mar, 2010


Bertie I didn't realise that the base was concreted in, It looks like it will withstand a gale you've done a grand and sturdy job, wish I had one lol

20 Mar, 2010

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