Thinking, no doubt, of some disastrous camping holiday experience or images of hurricanes in turbulent climes, many of those considering a polytunnel purchase seem to imagine that the structure might easily blow away. Do polytunnels blow away? Well, the short answer to this is no. You may be reassured to hear that as long as they are properly erected, polytunnels can withstand relatively windy conditions without tumbling off over the countryside, or ending up in a next door neighbour’s garden.
How Are Polytunnels Fixed to the Ground? Why won’t a Polytunnel Blow Away?
Unlike a tent, which could easily blow away in a very windy location, a polytunnel is not simply pegged lightly to the ground. Depending on the choices made at the point of purchase, and the surface on which the polytunnel has been constructed, the polytunnel will be firmly affixed to the ground by means of ground tubes and ground anchors, fixing plates (for hardstanding) or by ground tubes and trenched polythene. When the cover is trenched, the weight of a certain depth of soil will hold the structure down all around the edges. This will not only serve the hold the whole structure down but will also help make sure the cover does not blow away. (Trenched construction may be better than a base rail for a windy site.)
Can I have a Polytunnel in a Windy Location?
While a more sheltered spot is obviously ideal for a polytunnel, you can also position a polytunnel in a rather exposed and windy place, as long as you take certain measures to strengthen the structure. We would recommend that if you are placing your polytunnel in a windy location, that you opt for crop bars and additional storm bracing.
We would also recommend that you take extra care in making sure that the plastic is pulled taut over the structure and will not flap about too much. Flapping cover material is far more likely to be damaged in a strong wind.
Make sure that there are no branches or vegetation nearby that will whip against the polytunnel in strong winds. Twigs and branches could easily rip or tear the cover material in a gale.
How Can I Protect a Polytunnel From Strong Winds?
In addition to affixing extra bracing and cross-bars to your polytunnel to help it withstand windy conditions, polytunnel owners, potential and current, can also take other measures to help protect a polytunnel from being damaged on a windy site. Most effective of these measures is creating a wind break hedge, or a shelter belt of trees on a larger site. Planting can help to mitigate the risk to the structure from particularly strong gusts and can help to direct and diffuse the wind flow on site.
Deep-rooted trees are often best for withstanding strong winds, though of course which trees and shrubs will be best for creating your windbreak will depend on where you live and what the conditions of soil and climate are like there. What will work well in the south of the UK are not the same things that will work well in the Highlands of Scotland, for example. Clues may be garnered from observation around the area where you live. Other shelter belts and hedges can often be found edging nearby gardens and farmland and can give you a sense of the species that will work best for a windbreak in your area.
How to Create a Windbreak
Remember when creating a shelter belt or wind break that the aim is to break and disperse the power of the wind rather than stopping it entirely. If the trees are too dense the wind will build up on the windward side causing turbulence. If incorrectly positioned, the heat can build up on the inside of the windbreak and high humidity in summer could means more pests and disease problems for your crops. That said, it is usually the case that species will be placed more closely spaced than they would ordinarily be.
A wind break hedge of around 2m in height can protect an area behind it of around 60m (a ratio of around 1:30). It will also reduce wind on the windward side for a distance of around 2-4 times its height, as the wind will move upwards when it encounters the barrier before dropping down again. In both wind break hedges and shelter belts, the ratio of height to length of the planting area should be around 1:10, so, for example, if creating a shelter belt with trees 10m in height, the length planted should not be shorter than around 100m.
If you create an effective windbreak, a polytunnel can be safe and secure on practically any site. Even on the most blustery of sites, a polytunnel will not blow away, and is far less likely to get damaged in any way.
Sean Barker is the MD of First Tunnels, and is enthusiastic about providing quality gardening supplies to gardeners across the UK