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ALL FARMERS and growers, large and small, should consider the benefits of providing protection from strong winds. There are few holdings where there is no advantage in extra protection; on some sites it is essential in order to cultivate any crop at all to a good standards The smaller grower is likely to gain a lot more than large scale farmers, especially those of you that grow top and soft fruit and vulnerable vegetables.
The main advantages of shelter are:
Hedges and shelter belts are pleasing to took at, which is a good enough reason in itself.
As with all good things, there are a few drawbacks.
The main being:
There are several types of shelter. I shall deal first with temporary structures. These are non-living types, used primarily for short-term use or to shelter living trees and hedges to encourage rapid establishment.
The easiest type of material to erect is the woven plastic mesh type, usually green or black. This is available in varying degrees of porosity, the most suitable being about 50% which allows half of the wind to percolate through, which is important. A solid barrier will cause excessive turbulence on the leeward side. The ideal shelter is a filter not a solid screen.
Height is important and as a general rule the distance away from the shelter that is effectively screened is 10 times its height, for example, a screen 2m high will provide good shelter for a distance of 20m, beyond that the benefit becomes increasingly less. On slopes facing the prevailing wind the height will need to be greater depending on the degree of the slope.
Any form of netting needs good support. This takes the form of posts every 5 - 7m, these must be strongly "planted". The best sized hole is as near as possible the same size as the post, for posts 2m high bury 1m in the ground, and pro-rata for longer sizes. The cheapest supply of poles is from forestry thinnings, available in most areas
If you want them to last more than 5 years, the buried portion must be protected. The most effective and economical way is to partly fill an oil drum with creosote and stand your poles in this, as many as it will hold. Heat up the creosote by means of a fire or gas ring underneath until it is very hot, but do not boil! Allow the liquid to cool naturally. As the creosote cools the cells in the timber will contract and draw the liquid in. Be sure that the timber is as dry as possible and BE WARNED, this could be a dangerous operation if not done carefully, creosote is very flammable, be sure to have only a small fire and that the drum is standing securely on bricks. Cap the top with a piece of old lead or similar sheet material.
Horizontal wires need to be stretched very tightly at intervals to suit the width of the netting, but no more than 1m apart. Nail these with galvanised staples to the posts, do not drive the staples right home, leave enough to allow subsequent adjustment of the wire. Every 50m fix a type of wire strainer to the post, this can be used to take up the slack at a later date, as the wire will stretch once it has "done" a few gales.
Fix the netting with small lengths of thin wire wrapped around the netting and wire every 300mm.
This shelter should last for 10 years. It is no substitute for the real thing, but will certainly ensure rapid establishment of a shelter belt for the future.
A much lighter and movable structure can be made using battens {38 x 25mm) with a pointed end, every Em and a length of plastic baler twine top and bottom clipped to the netting. This can be held each end by a guy line and peg, intermediate lines can be fixed where needed from the top of the posts to pegs in the ground either side.
This is suitable to protect low polythene cloches and where shelter is needed temporarily. They could be used horizontally on short posts for the rapid drying of onions etc. the height need only be 1m, these can be placed at 10m intervals.
Another type of windbreak can be made entirely out of timber. This is in the form of 25 x 6mm battens nailed with galvanised nails (one each end) to a 75 x 50mm timber, which is fixed horizontally to the uprights, which should be no more than Em apart. Wastewood (slabbing) is usually available from such places as the Forestry Commission at low prices by the ton. If you have access to a large circular saw fitted with a rip-blade this windbreak is cheap and effective. Battens are spaced apart to give a gap of 25mm between. This allows filtration of the wind. Battens should be supported at approximately 1.2m centres.
The ultimate form of shelter. With the right varies you could have an effective windbreak 4m in 5 year certainly worth waiting for. s, It Is Plant between November and the end of March, avoid very wet or frozen ground. It makes a better job if You rotovate a strip the width of your plantings well in advance. Ensure trees are planted firmly into clean ground.
Trees will grow in quite poor soils providing they are a suitable variety and it should not be necessary to provide any nutrients, unless the ground is particularly barren.
Shelter belts comprise of large trees spaced about 2 - 3m apart in 2 or more rows staggered. The ultimate size will depend on species, for very large trees it will be necessary to thin every other one once they become overcrowded.
Once established shelter belts will provide much greater protection over a greater area than hedges and lower establishment costs. They are most suitably for larger fields where space is less of a problem. If possible new planting should be carried out well in advance of any existing trees reaching maturity in order to give the new trees a chance to reach a protective size before the existing gives out. This will be 20 - 30 years for most species.
Shelter hedges comprise of a much thicker barrier which will be kept to a tidy shape and restricted size by pruning, clipping or pollarding. They will be planted much closer together in single rows, trees at 300 - 900mm apart, and will be used to divide larger fields into smaller well protected units. Hedges are usually kept to a height of no more than 5m and a width of 1 - 2m. They require more regular maintenance than shelter belts, clipping of some varieties needs doing twice a year.
Whatever you decide to plant it is most important to use small specimens, not more than 1.2m high for protected sites and 0.7m for exposed sites. Conifers need to be much smaller, 1 - 2 year old seedlings raised in pots are ideal. larger specimens take much longer to establish and will rock on their roots in the wind, this will cause a smeared hole around the base and subsequent death of the tree.
Weed control is very important during the first two seasons when the roots are putting down their feet. Top growth will not be rapid during this period but after two seasons will become very rapid, with some species as much as 3m per year. l have found that a good mulch of straw 300mm thick around the individual trees or right along a row will keep grass down well, this will need to be topped up in the second year if weeds appear. Any material that suppresses weeds can be utilised, sawdust tree bark, F Y M etc. Black polythene (heavy guage) can also be used.
Deciduous trees make more rapid growth than conifers and provide a more permeable barrier. They are easier to establish, raise and cost less. Shelter hedges may consist more of evergreen shrubs and bushes, which naturally grow no more than about Em high.
Sources of planting material are many, the cheapest being obtainable for the effort of digging your own from woodland and waste ground. Sycamore, birch and alder being the most usual. Here in Cornwall the local council will provide trees free of charge and advise on suitable species for your area.
Similar schemes may operate in other areas, so contact the council for details. The Forestry Commission may have material at cheap prices .Grants are available from the Ministry.
The species below are suitable for both hedges and shelter belts. These are generally the most easily obtainable and provide the quickest cover.
Alder
(Alnus glutinosa). Very fast growing, very high tolerance to both salt and wind blast. Will grow to Em in 5 seasons given reasonable conditions. Prefers a wet site but does well in dry soils as well. Can be clipped to form a tight narrow hedge or left as a tree for larger shelter belts. Can be coppiced and pollarded, useful as firewood. Fixes its own nitrogen from the soil.
Birch
(Betula Alba). Fast growing, similar to the above in most respects except that it is not suitable for coppice or pollard work. Very graceful to look at and will thrive on the poorest soils or rock screes. Will provide a vast number of seedlings from about the fourth year onwards.
Sycamore
(Acer pseudoplatanus). Fast growing after the third or fourth year but slow initially, very easily obtained, many landowners are only too glad to get rid of them. Can be clipped, pollarded and generally mutilated with no ill effects. Tolerates wind and poor soil. Roots tend to spread widely.
Villow
(Salix). Many varieties available, the commonest being White Willow (S Alba) and Goat Willow (S Caprea). White is the fastest and thickest, can be kept very tidy, once established can put on am per year. Goat Willow is more tolerant of poor soil conditions and a drier environment. Both will appreciate a damp site.
Ash
(Fracinus excelsior). The common ash and the mountain ash (Sorbus aucuparia) are not related but are guise similar. Both are tolerant of high winds, grow fast and can be cut around to form the desired shape. S Aucuparia has a good crop of berries in the autumn. They are suitable for very poor soils.
Japanese Larch
(Larix Kaempferi). A deciduous conifer. Very attractive shape, grows rapidly to a conical shape with dense branches right to the ground. The needles appear very early in the spring and last until late in the year when they turn a beautiful colour. Will tolerate much wind, poor soil and moderate clipping.
The following species are suitable only as shelter trees, they will not tolerate clipping or heavy trimming. They are all conifers.
Monterey Pine
(Pinus radiate). Fast growing and very good against salt and wind blast. Suitable only in milder districts. Ages . ether fast, shallow roots that spread a long way.
Bishops Pine
(Pinus muricata). As above but more tolerant to colder areas.
Austrian Pine
(Pinus nigra austriaca). Tolerant to chalky areas, very good in maritime areas and fast growing.
Cupressus
Many different varieties are available. Most of the common ones are easily obtainable but they are usually quite expensive. Quick growing but tend to grow much too thick for good windbreaks, not easy to establish on exposed sites. Can be clipped to a very tidy hedge.
The following hedging plants can be clipped or trimmed to any size and shape. I shall not go into details of habrt etc as they are generally similar. Most are suitable for semi-protected areas and many will tolerate urn nosed conditions.
Bamboo, Berberis, Hawthorn, Eleagnes, Exallonia Elder, Hornbeam, Cotoneaster, Fuchsia, Holly, Privet Beech and Maple.
Further information on species and varieties are best sought from the Ministry Publications Department - give them a ring and they will send you several very helpful booklets. Hilliers manual of trees and shrubs is excellent for descriptions. "
IAIN TOLHURST
MOORVIEW STRAWBERRY FARM,
ST. AUSTELL. CORNWALL.
Copyright © 1984 New farmer and grower