Windy sites need not be overlooked completely as potential locations for a polytunnel. But very windy sites may require extra work to be done in preparation for the erection of the structure or structures. The most effective way to make a windy site suitable for a polytunnel is to create wind break hedges or shelter belts.
What Are Wind Break Hedges?
A wind break is simply a barrier of trees and/or shrubs that are positioned between the strongest winds on the site and your polytunnel. The aim of wind break hedges is to break and disperse the power of the wind rather than stopping it entirely.
While in a smaller, domestic scale setting, a wind break hedge will usually be sufficient, on farmland, larger shelter belts may well be required on windy sites. To be effective, shelter belts will usually include at least three rows of trees, which are staggered to maximise cover.
Tips For Creating Wild Break Hedges
Get the Spacing Right
If the trees/shrubs 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. Leaving 30-90cm between the trees or shrubs is generally considered to be optimal.
Consider Wind Direction, Not Just Property Boundaries
Construct shelter belts or wind breaks at right angles to prevailing winds, rather than along property boundaries. 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. To maximise this lifting and diffusing effect, it is best to plant to create a triangular cross-section, with tallest plants in the middle, bounded on either side by smaller plant species.
Follow the Right Ratio of Height to Length
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. Following this ratio will help to reduce turbulence around the ends of the windbreak.
Take Into Account the Shade Cast By Your Wind Break Hedges When Planning Your Garden
Don’t forget, when planning a shelter belt or wind break, to take into account the shade that it will create. Don’t position your polytunnel within the shade it casts, but slightly beyond it, in order to make the polytunnel as productive a growing area as possible.
Consider Other Uses of Your Wind Break Hedges
In a permaculture system, a wind break is never just a windbreak, but can also serve a whole host of other functions. For example, the wind break might provide firewood or wood for other uses, it may also be a place to forage fruits or other edibles. Furthermore, a shelter belt or wind break hedge could also be of benefit as habitat and food source for a range of local wildlife.
Choosing Trees & Shrubs For Wind Break Hedges
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.
Choose Wind Break Hedges Plants for Your Area
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 wind break hedge in your area.
Be sure to think about:
- The temperatures and general climatic conditions usually experienced where you live.
- The micro-climate of the site in particular (ie, any frost pockets etc.).
- The strength of the winds that you are trying to protect your garden against.
- Whether there is maritime exposure (if you are on or near the coast).
- The type, properties and pH of the soil in your garden.
Consider The Importance of Biodiversity
When creating wind break hedges, it is generally best to choose a number of different plant species. The more variety you can introduce in the planting in your garden, the more beneficial interactions you can generate between the various plants (and local wildlife) and the more resilient the garden ecosystem will become.
It is generally best to include a range of both evergreen and deciduous trees and/or shrubs, so that the wind break will be effective all year round, and will cater to as much wildlife as possible. Evergreens will, of course, keep their leaves all year round and continue to serve as a buffer against strong winds. But too solid a barrier could be detrimental. The branches of deciduous trees and shrubs can still filter the wind in winter to a degree, and the leaves that fall from them will rot down on the soil and feed the system.
Deciduous Trees & Shrubs For Wind Break Hedges
Some good options for wind break hedges include:
Common Alder (Alnus glutinosa)
Common alder is a deciduous tree. It will grow to an eventual height of up to 25m and will have a spread at maturity of 4-8m. The alder will grow well in a range of soil types and situations but it is particularly prized for being good in wet conditions and can be used in land reclamation.
Hornbeam (Carpinus betulus)
Hornbeam will grow into a large deciduous tree though can easily be kept to a smaller size. As trees, hornbeams can provide protection from winds in areas with moist but well-drained or well-drained soil. Hornbeam can also be made into a hedge for a more neat and formal look and could be a good alternative to beech hedges in exposed locations.
For smaller sites, large trees may not fit the bill. In such situations, small trees such as hawthorn may be a good option. Hawthorn trees will grow to an eventual height of 4-8m if their growth is left unchecked, though it should be noted that they can grow to a width of over 8m. Hawthorn is often best utilised as part of a mixed, wild, windbreak hedge.
Oaks are a favourite with many gardeners and fortunately, these sturdy and dependable trees will work well for a windbreak. Common oak (Quercus robar), turkey oak (Quercus cerris), sessile oak (Quercus petraea) can all be good deciduous options.
Hazel can be a tree or large shrub, and in addition to providing wind breaking, can also provide a yield of nuts. It is a quick growing option that can also be coppiced to provide firewood and other useful yields.
Blackthorn/ Sloe (Prunus Spinosa)
Blackthorns are great for windy situations. The sloes are also useful to humans as well as appealing to a range of native wildlife. Blackthorn will do well in any moist yet free-draining soil in full sun and have a bushy habit that is perfect to create a windbreak hedge that will protect the rest of your site.
Elder (Sambucus nigra)
Another shrub with edible berries (and flowers), elders are perfect for including in an attractive mixed shrub and tree windbreak. Elders are unfussy and will thrive in a wide range of different situations.
Berberis is another shrub that is particularly unfussy. There are a number of varieties to choose from that will do very well almost wherever you put them and are easily able to cope with the wind in an exposed location. An evergreen berberis will help provide a windbreak year round.
Elaeagnus x ebbingei
This versatile and useful nitrogen fixer can grow happily, even further north in the UK, though it will tend not to fruit in more northerly areas. One of the good things about this shrub is that it will grow well in less fertile soil.
This evergreen is another shrub that can help maintain cover from sea breezes in winter when it is often most needed. Pyracantha is attractive and can also help to attract birds and other wildlife to your site, which may be of benefit as you begin to establish the rest of your garden behind the wind break hedges.
There are, of course, plenty of other options to consider, and the more plants you are able to include in your wind break hedges the better. Plan well, and your planting should protect your polytunnel and other elements in your garden for many years to come.
Do you have any tips to share? Please feel free to do so below.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.