How to build a polytunnel for (about) £150

February 15, 2011 § Leave a comment

Ok it might end up looking a little ‘Steptoe’, but you’ll have fun building it. I did one of these last year and its still standing, though I am going to rebuild it using more hoops to make it stronger.

Most of the cost here is for good polytunnel polythene- the rest of the component parts can be cobbled together for free.

A nifty way to make a tunnel cloche at home is to cut some long, young saplings or bendy (willow) branches, ideally more than 6ft in length. They need to be a uniform thickness along the length of 1-2” with side shoots removed and the join smoothed over. Soak them in water for a week (wrap in a wet blanket, unless you have a pond) to make them pliable then wedge them into an ‘A’ shape between a space which is between 1.5 and 2m wide- a stepladder is quite good for smaller frames- and leave them dry thoroughly- for at least 1 month.

A quicker option is to use flexible plastic tubing (the PEX type used for plumbing) which can slot directly over the stakes (read on for staking info). Screws can affix the tubes to the stakes to make a reasonably sturdy structure.

Purchase polytunnel plastic or netting (fleece is a cheaper option but tears easily) and anti-hotspot tape or gaffer tape. If your arches are 1m high and 1.5m wide at the base you need to buy polythene which is at least 3.5m wide.

Dig two trenches about 1.5m apart each 30cm (12”) deep and 30cm wide (a spades width). Hammer 60cm (2ft) stakes into the ground 1.6m (5.2ft) apart at 0.75cm (2.5ft) intervals along the outside of the trench. Leave half of the stake above ground. The stakes secure the structure and could be replaced by the sides of a raised bed or railway sleepers. Stakes can be made from offcuts of wood, metal plant stakes, metal pipes or rods, thick tree branches.

You want to put each arch 0.75m apart, so however many arches you have multiplied by 0.75m equals the length of your trench. You just push the end of the arches into the soil to a depth of about 20-40cm (10-24”) next to the stakes. bind them to the stakes for added support. If using PEX tubing slot them over the stakes.

Drape your covering over the structure. Roll up a bamboo cane along either long edge of the plastic and secure with tape. Bury one side of the polythene into the ready dug trench (the bamboo helps to keep it taught and reduces the likelihood of it being blown around considerably). Wedge the other side it gently between the stake/edge of raised bed and the arch. Secure with plenty of tent pegs, specialised polytunnel pegs or smooth rocks and to avoid the polythene tearing put tape at these sites of friction. At each narrow end gather the polythene tightly into a neat ball and tie it with thin rope. Tie the rope to a rock.

When you need to go into your polytunnel you can simply raise the bamboo cane and balance it on top of the structure. To ventilate, untie the bunched end from the rock and re-bunch it and retie it at the top of the structure.

If anyone has a better method (likely) please send it in.

Click here for an excellent link which shows you how to build a full size polytunnel.

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