How to build a polytunnel

How to build a polytunnel

A polytunnel will enable you to to bring a slice of the Mediterranean home, increasing the variety of crops you can grow. Find out how to build your own, in our guide.

A table displaying which months are best to sow, plant and harvest.
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To do
To do

Do To do in January

Do To do in February

Do To do in March

Do To do in April

Do To do in May

Do To do in June

Do To do in July

Do To do in August

Do To do in September

Do To do in October

Do To do in November

Do To do in December

Building your own polytunnel from a kit can save you hundreds of pounds in construction costs. All you need are some basic DIY skills and some willing helpers – four people is ideal.

Choose a warm day to install the cover. Warm weather makes the plastic more pliable and therefore easier to stretch tightly over the frame. Before assembling your kit, ensure the site is level. If your site is exposed, you might wish to put up fences, screens or even hedging. When the kit arrives, check thoroughly that all components are there, and read the instructions carefully.

Choose a warm day to install the cover. Warm weather makes the plastic more pliable and therefore easier to stretch tightly over the frame.

Once the structure is up, add a path, if necessary, using paving slabs, bricks, or self-setting gravel edged with timber. Where you intend to plant direct into the border soil, fork it thoroughly to relieve any compaction and incorporate plenty of compost. Alternatively, if you’ll be growing in pots and growing bags, or on benches, firm the soil, cover with black polythene or weed-suppressing fabric and top off with gravel to create a hard-standing area.

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You Will Need

  • Polytunnel kit from supplier
  • Cement, for foundation tubes if required
  • Hammers
  • Wooden block
  • Adjustable spanners
  • Screwdrivers
  • Spirit level
  • Anti hot-spot tape

Total time:

Step 1

How to build a polytunnel - adding the foundations
How to build a polytunnel – adding the foundations

Correctly placed foundation tubes will ensure the stability of your polytunnel. Use an anchor plate with the tubes (shown above) if fitting a base rail – see step 3 – or on exposed windy sites. You can also cement in your foundation tubes. Mark the base positions, making sure they’re evenly-spaced and check all the angles are square. Then drive the foundation tubes into the ground, hammering onto a wooden block to avoid damaging them.

Step 2

How to build a polytunnel - adding the support structures to the hoops
How to build a polytunnel – adding the support structures to the hoops

Connect the separate hoop sections together, then slide the ends over the foundation tubes. Fix the support struts to each hoop. Always check the positioning of bolts and other fittings before you attach them, making sure they won’t rub against the cover and cause it to tear. Finally, fit the ridge pole, corner bracing and door frames. Check that the hoops are all straight and in line, then tighten all the joints carefully.

Step 3

How to build a polytunnel - bolting in the foundation tubes
How to build a polytunnel – bolting in the foundation tubes

There are two ways to hold the plastic cover in place: pinning it to a wooden base rail which is fitted to the foundation tubes; or burying a skirt of polythene in a trench 30cm deep. A base rail is the easier way, particularly if there’s not enough space around the polytunnel to dig out a trench. If your model is supplied without a base rail, you can make one using lengths of 70 x 45mm timber, cut to length, then bolted on to the foundation tubes.

Step 4

How to build a polytunnel - anti-hot tape
How to build a polytunnel – anti-hot tape

Anti-hot spot tape is used to create a layer of protection between the polythene cover and the metal hoops, which can become hot in summer. This prevents heat degradation of the cover and can increase its life by over a year. You can buy anti-hot spot tape from most polytunnel/greenhouse suppliers. Place a strip along each hoop before fixing the cover in place. Clear any stones from the ground and unroll the cover, sliding it over the hoops so it sits evenly over the frame. Fix it to the base rail or bury in a trench. Keep the plastic taut when fitting. Cut it to fit the doors by making a v-shaped flap.

Step 5

How to build a polytunnel - fixing the door
How to build a polytunnel – fixing the door

Just in case the wind picks up overnight, it’s best to fit the doors on the same day as the cover. Start by making the frames for all the doors and covering them with polythene. Sliding doors hang from a runner attached to the top of the door frame, while hinged types are designed to swing on one side of the frame. Hold the door in the frame before attaching it, to ensure you hang it squarely in place, so it fits the opening correctly.

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