Polytunnels offer the commercial grower a suitable environment for many varieties of fruit, flowers and vegetables, with the advantage of being able to cover a large area of ground relatively inexpensively compared to glasshouse cultivation and its high maintenance costs. The correct siting of a polytunnel, whether domestic or commercial, is critical in order to achieve the highest possible yields from produce whilst keeping the polytunnel in good condition.

Ensure the site is level

The site should be level and prepared by a landscaping contractor if possible. A fall of 1:100, or a one-metre drop over one hundred metres, is acceptable for a commercial polytunnel which will require the main stanchions to be concreted in. If a greater slope is unavoidable, then the polytunnel should run down the slope if possible, not across it. Slopes could cause problems during erection, or result in the need for differing soil levels inside the tunnel, which may interfere with the planned growing conditions. North-facing slopes will lessen the amount of light reaching the polytunnels and should be avoided if at all possible.

Consider wind strength and direction

The dominating factors when siting a polytunnel are wind direction and its strength. The prevailing wind direction in the UK is south-southwest, at around 245 degrees, though obviously wind direction at any time is variable. If the planned location is on an exposed site, then the polytunnel needs to be positioned with the sides facing into the prevailing wind direction, rather than the ends. This will allow the wind to blow over the polytunnel rather than gust through any openings. If excessive wind exposure is unavoidable, then windbreaks should be considered, either from hedging, fencing or trees, although the latter should not be too close to the polytunnel in order to avoid the possibility of tree roots interfering with digging operations.

Clear the surrounding area

Adjacent trees may also present problems from falling branches and excess shading, as well as leaf mould, sap and honeydew from tree insects leaving a sticky residue on the surface of the polytunnel, which will reduce its absorption of available light and heat. It is important not to have any gaps in the windbreak as the wind will increase speed as it passes through the gap, resulting in it hitting a more targeted area of the polytunnel, resulting in damage. Similarly, the commercial polytunnel should not be erected in a valley between two hills, as the same funnelling effect will occur as the wind accelerates through the valley. This is especially important should the site be subject to heavy snowfall and drifting.

Ensure enough sunlight can reach the polytunnel

Sunlight will be the chief source of heat within the polytunnel. Even on a cloudy day, the polytunnel covering will absorb some radiation. Windbreaks need to be high enough to deflect wind flow, but low enough to prevent light interference and excessive shading. The traditional arrangement is to position the polytunnel from east to west, which will track the path of the sun as it crosses the sky from dawn to dusk, although a north to south orientation is acceptable.

If you need any more information or advice on siting a commercial polytunnel then please don't hesitate to contact a member of our sales team by emailing sales@npstructures.co.uk or calling us on 01282 873120.