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.
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.
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.
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.
If you feel uncomfortable inside the poly tunnel, most likely your plants will too!
There is a lot more to say on this topic. If you have any questions or are interested in attending a similar workshop, please contact Nevil directly.