I’m in the process of designing my latest attempt at a truly indestructible polytunnel. Our allotment is on the side of a hill at the top of a valley that faces the sea. The winds we get in winter are incredible. One of my attempts at a plastic greenhouse was ripped to pieces, including shearing of metal tubes. The next blew out of our allotment, over the 8 foot fence enclosing the allotments, across a field and into the side of the nearby racetrack. So when I say it’s windy, I do really mean it.
The most, read as only, successful attempt has been a smaller polytunnel with many hoops and strong stakes to hold it into the ground. I’m currently trying to scale up this design to a 2m high 2m wide 3.5m long polytunnel. If you’ve seen large polytunnels made of blue tubing on an allotment this stuff is 50mm MDPE plastic water waste tubing. If you’ve seen little cloches/polytunnels it’s probably 25mm MDPE water supply tubing. It’s dead easy to get the 25mm stuff secondhand, people are always trying to get rid of it; the 50mm is much more expensive and a lot harder to find secondhand.
I have picked up tons of the 25mm but it’s just not strong enough to make a 2m wide tunnel, so I had the bright idea of zip tying 3 lots of 25mm pipe together to form a 3 ply pipe. This was half successful. It is much more stable and strong than the 25mm but not strong enough the hold the full circle shape from my original design (right).
Instead I’m now going to need to use 1.8m stakes driven into the ground at 1m spacing and use the blue piping to create the arch only. This will also allow me to add spacers between the posts and the doorway to help strengthen the doorway structure; as well as saving on pipe!
Details of the stakes I intend to use are below, I’ve used Suregreen posts before and they are incredible value for money.