Advice on Polytunnel Purchases

Best Polytunnel For Windy Site: Planning & Structure

Last Updated on February 15, 2022 by Real Men Sow

Polytunnels are wonderful structures and have good value compared to greenhouses. Once erected they will be there for several years, so check out my tips before buying one. Polytunnel for a windy site can come in as a challenge so we’ll discuss that in this article too. 

Polytunnel

How Big Should Polytunnels Be For Windy Sites?

You should try to fit the largest plant you can in your space. This is because it’s useful for drying and washing, as well as for growing. A tunnel always has more plants than it can hold. The hoops are spaced 5-6 feet (11.5-11.8m) apart, so the length can be multiples of this. 20-30 feet seems to be a good length for ventilation. Tunnels that are 60 feet long can have pockets of unventilated air.

Orientation of Polytunnels

  • North to the south is the ideal direction so that high crops in summer provide equal amounts of shade on either side. This also helps to reduce summer heat.
  • An east-west structure faces the sun, which is undesirable in hot climates. This also results in some shading of the northern bed, which is necessary when summer crops are taller in the middle.

Any orientation is possible. It is important to align the tunnel on any slope. Mulch and beds that are spread across slopes are more difficult to water. Also, it is important to have the doors at easy points so you can water them easily.

Ventilation of Polytunnels For Windy Sites

Fresh air is essential for plants, therefore, they should have plenty of it. The air in a polytunnel moves from one end of the container to the other. It is suggested to leave at least 6 inches (15 cm) between the top of the doors and the frame. This will allow for a little more airflow and carbon dioxide to enter the greenhouse.  

Side vents lower the temperature in windy conditions, and doors at both ends allow for enough fresh air to enter. It is cheaper and easier to cover the hoops only with polythene, at ground level or below. Side vents should be kept open for long tunnels that exceed 40-50 feet in length (13-16m).

Should the Polytunnels be attached at ground level, or buried?

To create a polythene barrier,  it is recommended that you bury the polythene in trenches one spade deep. This will protect against:

  • Pests such as rats, slugs and cats can enter, including rabbits, slugs and dogs.
  • Weeds are starting to creep in, including buttercup, couch grass and bindweed
  • Too much drought and too little cold air around the leaves of plants.

Attaching polythene to rails or battens at ground level is often easier than it seems. This means that you will need to dig holes for foundation tubes rather than just putting them in. You may also need concrete for windy locations. You will need to spend extra money on fixings, but they are worth it if you don’t have the space to dig a trench

Foundation of Polytunnels

To bury polythene in a trench, the tubes should be hammered into ground around 12-18in (30-45cm). Their role is to give the structure some rigidity. The tubes will not hold the structure in place when polythene has been buried. Instead, they will keep it stable in the wind.

This is in contrast to the fact that polythene attached to a rail rather than buried has a greater importance. Foundation tubes are more important as they hold the structure in place. You will need to install metal brackets on the ends of the tubes and dig a hole. Sometimes concrete may be required.

Crop Support Bars of Polytunnel For Windy Site

These are an “extra”, but It’s best to still buy them. They can be used to support climbing plants, from tomatoes and cucumbers to beans or melons. They are approximately 6ft (2m) tall and can be walked side by side.

When to do re-cladding?

The Polythene should be replaced every 5-8 years depending on how windy the site is and how tightly you can stretch it. It is easier to tighten polythene when it is covered in warm sunlight.

Kind of Polythene to Use

There are many types available, making it difficult to choose. Tunnels with anti-condensation or thermic polythene are on the expensive side. However, It isn’t worth the extra expense. The standard, light-diffusing version of polythene allows for around 89% daylight. Use horticultural grade, which contains a UV stabiliser. Without it, it will be brittle and eventually break in a year.

Polytunnel Doors

These are very useful and well worth the money when you plan your polytunnels for windy sites. It is possible to make your own. This is the place where you can be your most creative, especially if carpentry is your passion. 4×2 timbers work well for door frames.

Watering

Hand watering is the preferred way, but it takes more time. You can use two spray lines but don’t use them very often because it may have an uneven distribution. You’ll still need to water manually in dry areas.

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