Poly tunnels on a budget

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Landscape and gardens, Practical advice and DIY

Last week, on a beautiful Saturday morning, I drove 20 minutes north-west of Launceston to attend a workshop on Poly Tunnels. It took place at Tasmanian Natural Garlic & Tomatoes, Nevil Reed’s farm in Selbourne. Nevil grows hundreds of varieties of tomato in his poly tunnels.

A plastic-covered polytunnel with open doors, showing plants and containers inside. Two people stand outside on the grass under a clear blue sky. Trees and a green building are visible in the background.

A group of people stand outside a large glasshouse with a plastic covering, observing and taking notes on a sunny day with a clear blue sky and trees in the background.

Nevil has been researching, designing and building poly tunnels for the last nine years. His tunnels are all low cost, durable designs, aimed at mitigating against a variety of weather extremes.

The main reasons why you would like to build a poly tunnel is that you can extend your growing season, have better fruit earlier and longer, and also be able to grow more varieties of plants. On the other hand, because of the closed environment you will create, a little problem in your garden can become a big problem inside the poly tunnel. So you will have to monitor what happens a lot more and react a lot quicker.

There are a lot of different possibilities when it comes to choosing the kind of construction that you want. Like anything, cost is the big issue and also the durability of your construction. Do you want post and concrete in your garden? In any case you will have to brace your structure.

A large white glasshouse with a rounded roof stands on a grassy field under a bright blue sky with scattered clouds. Trees are visible in the background.

Inside view of a polytunnel with plastic covering, arched metal supports, and raised soil beds with plants growing along the centre. Sunlight filters through the translucent roof.

A row of large, white, arched polytunnels stands on a grassy field under a clear blue sky, with trees visible in the background.

A plastic-covered polytunnel stands on green grass under a clear blue sky, with trees visible in the background.

A large, white, plastic-covered polytunnel stands on a grassy field under a clear blue sky. An orange traffic cone and a small bucket are on the grass near the entrance.

A person adjusts the support structures of a transparent greenhouse tunnel, which covers rows of green plants on a sunny day with clear blue sky and surrounding trees.

A large, white, dome-shaped glasshouse structure stands outdoors on green grass, with a clear blue sky above. The glasshouse is secured with ropes and has some plants visible inside at the top.

Close-up of a blue and white rope tied in a knot around a green metal post, securing a sheet of clear plastic. The ground is covered with green grass and clover.

First thing to consider is the plastic. It needs to be UV stabilized and light enough to work with. For the thickness, choose 180UM instead of the 150UM. You do not want clear plastic. The more the light is diffuse, the better (70% to 80% is fine).

You also have to choose between poly or steel for the arches. The advantage of the poly is this is easy to bend and work with. If you choose to go for a tunnel with post, the steel will be the way to go. In a more lighter version using the poly, Nevil recommends using steel at both ends and tightening all the hoops at the ridge for better stability.

A blue and yellow rope tied around a large black pipe with green stripes, set against a clear blue sky.

A person stands in a garden with metal arches and rows of plants, adjusting or inspecting the structure. Two polytunnel greenhouses are visible in the background, set against a clear blue sky and trees.

The temperature inside a poly tunnel can be very high. Being able to control the air flow when needed is crucial. The side of the tunnel needs to be open almost every morning. The higher your tunnel, the easier it is to control the temperature inside the poly tunnel.