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Coastal Windbreaks & Hedges
How & Why |
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There can be no doubt that having protection from salty gales will greatly increase the possibilities for a coastal garden The wider, taller & deeper any protective screen from the wind is, the more protection it will give.
For those gardeners & prospective gardeners with enough patience & space a tall wide and layered Windbreak of trees & shrubs will offer the best protection. The more impatient gardener, with less room to spare or who is more concerned with keeping the view unobstructed should plant Hedge as broad & to be as tall as is practical. |
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Definition of a windbreak For our purposes a windbreak is a layered barrier of mixed shrubs and trees placed to protect a garden from strong salt-laden winds The role of a windbreak Windbreaks exist to bear the brunt of the wind and salt, anything else they do is a bonus (or a bane), they save your plants, stop the gales howling through your windows and you from being blown over when you go out the door. Siting & selecting the makeup of your windbreak Site your windbreak in the wrong place and the wind can still get in. Select your windbreak species carefully consider the site limitations, i.e., what will grow there. Remember that you want the windbreak to thrive and look good so it has to be well suited to the site. How high do you want it to be, don't plant a line of pine trees in front of your window and expect to keep the view. The amount of room you have for a windbreak is also important, in short the more room you have the more effective windbreak you can make. A solid wall of vegetation is not desirous, the wind hits it and Is forced over the top, so raising the pressure, behind the air pressure is lower so the air is sucked down where it swirls into damaging eddies (see Fig. 1). Slowing the wind with a layered defence is the best approach, but this is more costly in both space and plants. A front of shrubs followed by open crowned trees with a light under-storey of shrubs several meters deep will give the best defence. In such cases the wind is slowed all the way through so little eddying occurs (see Fig. 2). |
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Whatever kind of windbreak you erect it can only protect a certain area. As can be seen in both Figures 1 and 2 that the wind sweeps back down & in fairly quickly after passing the windbreak. It is possible to calculate approximately the ultimate 'Protected zone' behind a windbreak by multiplying the estimated final height of the windbreak by 5 to as much as 10 and there will still be a perceptible reduction up to 25 times the height away. These figures work for level sites only, slopes can greatly foreshorten these figures and create turbulence of their own. One can plant the tallest windbreak ever erected but if it is only a couple of trees wide there will be little benefit other than immediately behind as the pressure difference causes the wind to diffract (curl-in) around the edges (Fig. 3) A very deep windbreak confers little extra benefit, as it is the first few meters that create the 'protected zone'. Such a deep system is more of a woodland with calm air below the canopy but it will be windy again just a short distance past the leeward side of the stand. However a deep windbreak is less vulnerable to having gaps opened up by severe gales. |
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Finally windbreaks should be erected perpendicular to the prevailing wind for the greatest effect. The above model is the ideal and is not practical for many requiring as it requires considerable room and time to reach full effectiveness. Most people will at best be only able to plant a stout hedge, though not offering protection as comprehensive as the above they still make a great difference. |
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Fig. 1. With a solid windbreak much damaging turbulence is caused behind by large pressure drop |
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Once a wind break is established the difference inside is quite startling, the micro-climate created is mild and more humid and with a bit of shade luxuriant growth can be obtained and spectacular plants such as the Madeiran shrubby foxglove, Isoplexis sceptrum, or the Himalayan blue poppy, Meconopsis ‘Lingholm’, can be grown. Many plants that don't seem obvious make excellent hedges or windbreak components, New Zealand flax, Phormium tenax (right) is particularly impressive as a hedge and is useful in a really wet soil where it makes a thick barrier to the wind . |
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Your windbreak is also part of the garden, and should have some aesthetic merit in it's own right. Here Brachyglottis 'Drysdale', Olearia cheesmanii & Hebe x franciscana ‘Lobelliodes’ show that they can do more than just stop wind. |
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Hedges For large gardens smaller hedges can be used provide protection from winds in other directions while a large windbreak protects from the most damaging quarter. In smaller gardens a hedge is likely to be the main protection from the wind. When selecting the variety or varieties for your hedge you must first decide how you want to keep it, do you want a fairly loose and informal hedge, then shrubs such as Berberis are good but if you want a squared off or pruned hedge then Escallonia, Griselinia or Fuchsia may be more suited. Evergreen is good as it gives full protection year-round, attractive flowering varieties such as Escallonia rubra ’Crimson Spire’ or Olearia macrodonta are invaluable as they also contribute to the aesthetic value of the garden. Use of native species such as hawthorn or gorse adds to the wildlife value, but be aware that not all wildlife is to be encouraged into the garden, just ask anyone who has apple or plum trees for their opinion of bullfinches! Choosing a vigorous variety and vigorous specimens is also important as you want them to grow up as quickly as possible in the full exposure and to sprout back quickly from pruning. A third approach is a to form a series of mini windbreaks over a whole area, creating an overlapping and discontinuous canopy of trees and shrubs so filtering the wind as it passes through their crowns. However if such as scheme is poorly executed and the plants placed too far apart then the wind will funnel between them and destructive vortices will form. Another option still is to not try and stop the wind but instead garden with it, there are still a great many excellent plants which will thrive without the slightest protection. Check out the page on Coastal Gardening for more on this.
For a hedge the same principals as for a windbreak apply, the taller a hedge the more effective it can be. The following is a list of trees and shrubs suitable for use in windbreaks on the West Coast of the British Isles and their approximate typical final size; height by girth for trees, height by spread for shrubs. Please bear in mind that you are unlikely to see these trees reach this height but others will, so don't plant lines of them just a couple of feet apart. In exposed sites trees will be slower to grow and their final sizes will rarely be as large as those in more favourable situations. The below tree sizes are for those in such ideal situations so that you may judge the absolute maximum size they are likely to attain. There is a great variation in vigour amongst these plants; selecting species of similar growth rates should prevent some being swamped |
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Trees: Conifers: Monterey Cypress Cupressus macrocarpa 25 x 5m Common Larch Larix decidua 30 x 5m Sitka Spruce Picea sitchensis 30 x 7m Beech Pine Pinus contorta var. contorta 10 x 5m Mountain Pine Pinus mugo 2-8 x 10-3m Bishop Pine Pinus muricata 25 x 7m Austrian Pine Pinus nigra ssp. nigra 30 x 6m Crimean Pine Pinus nigra ssp. pallasiana 30 x 6m Corsican Pine Pinus nigra ssp. laricio 30 x 5m Maritime Pine Pinus pinaster 15 x 4m Monterey Pine Pinus radiata 30 x 7m Scots Pine Pinus sylvestris 20 x 7m Douglas Fir Pseudotsuga menziesii 30 x 8m Broadleaf trees: (Some suitable for clipped hedges) Prickly mimosa Acacia verticillata 5 x 3m Sycamore Acer pseudoplatanus 20 x 8m Italian Alder Alnus cordata 10 x 4m Common Alder Alnus glutinosa 15 x 4m Grey Alder Alnus incana 15 x 4m Sitka Alder Alnus viridis var. sinuata 4 x 5m Pacific Madroña Arbutus menziesii 15 x 4m Strawberry Tree Arbutus unedo 1.5-8 x 1-4m River Birch Betula nigra 10 x 4m Silver Birch Betula pendula 15 x 4m Downy Birch Betula pubescens 15 x 4m Himalayan Tree Cotoneaster Cotoneaster frigidus 6 x 3m Tasmanian Snow Gum Eucalyptus coccifera 10 x 7m Mountain Gum Eucalyptus dalrympleana 25 x 4m Tasmanian Blue Gum Eucalyptus globulus 25 x 4m Cider Gum Eucalyptus gunnii 25 x 4m Gippsland Mallee Eucalyptus kitsoniana 5 x 4m Smithton Peppermint Eucalyptus nitida 10 x 5m Ghost Gum Eucalyptus pauciflora ssp. niphophila 6 x 5m Risdon Peppermint Eucalyptus risdonii 6m x 4m Beech Fagus sylvatica 20 x 10m Ñirre Nothofagus antarctica 10 x 3m Goat Willow Salix caprea 10 x 7m Osier Salix viminalis 10 x 5m Whitebeam Sorbus aria 10 x 3m Rowan Sorbus aucuparia 10 x 3m |
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Shrubs: (Many of these are also suitable for hedging) Coast Wattle Acacia sophoriae 2 x 3m Baccharis patagonica 1 x1m Bedfordia linearis 2 x 2m Berberis darwinii 2 x 2m Berberis linearifolia 2 x 2m Berberis verruculosa 1.5 x 1.5m Berberis x stenophylla 3 x 3m Brachyglottis rotundifolia 3 x 3m Butterfly bush Buddleja davidii 2 x 3m Orange ball tree Buddleja globosa 2 x 3m Larger Ceanothus can be used to brighten up a windbreak if they have some protection around them. Fachine Chiliotrichum diffusum 1.5 x 1.5m Taupata Coprosma repens 3 x 3m Corokia species & hybrids 1-3 x 1.5m Correa backhouseana 1.75 x 2m Hawthorn Crataegus monogyna 2 x 2m Brooms Cytisus spp. can add colour 1-2 x 1-2m Tasmanian Pepper bush Drimys lanceolata 3 x 2m Elaeagnus x ebbingei 2 x 2m Escallonia rubra 3 x 3m Many Escallonia hybrids, mostly with E. rubra blood, are excellent even in very exposed situations. 1.5-4 x 1.5-3m Papauma Griselinia littoralis 15 x 6m Coast Koromiko Hebe eliptica 2 x 2m Hebe parviflora 3 x 2m Willow-leaf Koromiko Hebe salicifolia 3 x 2m Hebe x franciscana ‘Lobelliodes’ 1.5 x 2m Manuka/Tee tree Leptospermum scoparium 1-5 x 2m Bearberry Honeysuckle Lonicera involucrata 3 x 4m Olearia albida 2 x 1.5m Olearia arborescens 2 x 2m Olearia avicenniifolia 3 x 3m Olearia capillaris 2 x 2m Olearia cheesmanii 2 x 3m Olearia x hastii 2 x 2m Olearia lineata 'Dartonii' 4 x 2m Olearia macrodonta 'Major' This is the mainstay of a West Coast Windbreak it is tough, quick & adaptable. 3 x 3m Olearia x oleifolia 'Oleifolia' 1.5 x 2m Olearia paniculata 4 x 2m Olearia solandri 2 x 2m Olearia traversii 4 x 2m Ozothamnus spp. from New Zealand 2 x 2m Ozothamnus rosmarinifolius from Australia 2 x 2m New Zealand Flax Phormium tenax 3 x 2m Coast or Mountain Flax P. cookianum 2 x 2m Rhododendron yakushimanum For adding colour 1.2 x 1.5m Many 'Yak' hybrids are also well suited to windy places. Japanese Rose Rosa rugosa 1.5 x 2m Swiss Willow Salix helvetica 1.5 x 2m Woolly Willow Salix lanata 1.5 x 3m Double Gorse Ulex europaeus ‘Flora Pleno’ 2 x 2m |
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Olearia macrodonta, tough quick & attractive it is an invaluable plant for the coastal garden |
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This list is far from complete but includes most of the common and many of the best plants for West Coast windbreaks. We try to offer as many of these plants as we can, as well as hundreds of others. If you plan to plant a windbreak come and see us and we will be glad to advise you on the best choices for your site.
Erecting a Windbreak or Hedge |
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Fig. 4. Two sample layouts for a windbreak in an exposed site of 3 layers. On the left, 1st a fence of windbreak netting to aid establishment, then 2 offset rows of vigorous tough shrubs & a row of hardy pine trees or similar. On the right, the same tough the line of trees is straddled by two rows of shrubs, as the trees mature they will look to be under planted by the shrubs. As the front ranks establish further layers can be added behind so strengthening & eventually heightening it. |
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Olearia traversii, a quick growing & very tough large upright shrub with leaves glossy green above & shinny silver below. A 1st rate hedging plant. |
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Fig. 5. A sample hedge layout which will give a good stout hedge within a few years. The addition of a second offset row will increase the speed at which the hedge thickens-up, but doubles the cost. |
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Fig. 6. A 'Cornish Hedge'. Common in that county, is a stout earth filled dyke with tough shrubs planted on top. |
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The erection of a hedge or windbreak involves basically the same procedure, with a windbreak simply being deeper, with more rows. A hedge could be planted and later 'upgraded' to a windbreak by adding more shrubs & trees behind.
Protective Fencing First chose the site for you windbreak or hedge, ensure it is secure from livestock & deer or that the fence you will lay out will be. A single nights browsing can destroy several years growth. Lay out a line slightly greater than the length desired (same principle as Fig. 3.). Drive in fairly stout treated softwood posts around 1.2m (4’) apart. On the windward side attach at least three running wires from the top bottom & middle of the posts, then clad with a roll of synthetic windbreak fabric at least 1m high, different products are affixed by different means. Around 60% wind reduction is desirous. This barrier provides important extra protection for the planting in the vital first couple of years of establishment, without which the growth will be considerably slower. However in less exposed sites or if money is tight & time not short, the netting maybe forgone. For the windbreak material there are quite a variety of types, Netlon, Tensar, Paraweb & the cheapest, knitted polythene monofilament (like a tough plastic hessian it is usually only good for about a year in very exposed sites, though this is usually long enough) are the most common materials. Alternatively you could construct temporary hurdles of woven hazel or willow coppice shoots also old New Zealand flax leaves are durable & easily woven, though for these the uprights must still be strong & firm. Any protection will often follow the line of an existing boundary fence the netting may be mounted on it if the position & nature of the fence is suitable. This saves a lot of money & effort, so if practical it should be taken advantage of. A third alternative is 'Yorkshire boarding' this will be familiar to farmers as it has long been used for sheltering livestock. A line of Deerposts have lengths of treated sarking board (12' x ¾') firmly mounted, alternating in front of & behind the post as they go up. This baffles the wind as it passes, however though effective it is very costly in materials, i.e. it needs a lot of wood. Though if there is a sawmill nearby & you have a trailer you maybe able to get for free the outer curved slabs that are cut off the timber when it is sawn square. These are rather irregular in shape & untreated so they will not last long. If possible select Larch slabs, these hold onto their more attractive grey fissured bark longer & will last much longer than the more common Sitka spruce. Another method of more instant hedging, rarely seen in Scotland is 'Cornish Hedges' (see Fig. 6) where a stout earth-filled dyke is built along the boundary to a height tall enough to stop sheep reaching the top, say 5-6' and on the top two rows of tough & drought tolerant shrubs are planted, these should be bushy varieties that shouldn't get too high as you don't want them blowing out. This was a common method in the past when labour was cheap, a highly labour intensive task it would cost a great amount to employ someone to erect a Cornish Hedge. Fuchsia & Escallonia were commonly used in Cornwall, Hebe x franciscana ‘Lobelliodes’ is well suited, Corokia x virgata 'Red Wonder' would look good in this role as it's silver-baked leaves would look good viewed from below. In an open site with many rocks it is a good way of clearing them but drystone dyking is not easy to do well & help should be sought. Turf dykes have also been used in this way & are simpler & quicker to construct.
Drainage Ensure that your chosen site doesn't turn in to a bog every time it rains. There are plants which will tolerate waterlogging but growth & establishment will be far quicker if drainage is improved, don't over do it though, plants need moisture & growth is arrested when they can't get any. Ensure that the plants can be watered in times of need, either by hose or a watering can as a little help through their first summer will soon be repaid.
Type of Plants In all cases planting young plants will be better in the long run. If planted when young the plant can form the whole of its root system & top growth to suit the nutrient & water availability as well as the force & prevailing direction of the wind. However Very small plants will be easily swamped by weeds or succumb to drought in their first summer. Use entirely container grown shrubs (preferably in 1L or 2L pots) as planting shock will be negligible compared to that of field-grown or 'containerised', i.e. field-grown, then recently lifted & potted. Planting of evergreen container grown plants in exposed sites can be carried out from April until September, outside of this time the temperatures too low & gales to frequent for much establishment to happen. |
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A late summer gale blowing in from Antarctica at Mason Bay on Stewart Island, south of New Zealand. The 8½ mile long beach is backed by many familiar shrubs such as Brachyglottis rotundifolia, that thrive in our gardens 12,000 miles away. |
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How To Plant At least 60cm back from your fence line mark out your first line of shrubs. String a straight line from before where the first plant in the run will be until just after the last . Planting distances vary from species to species & site to site but planting 1m / 4'4" (no less than 75cm, no more than 1.5m for a hedge) apart (see Figs. 4 & 5).should do just fine in most exposed situations & give a good screen in a few years when using appropriate vigorous species The planting holes should be dug to at least twice the width & depth of the plants root ball. Amelioration of the existing soil with some well rotted manure or good garden compost will help. If these are unavailable a small handful of Blood, Fish & Bone Meal divided between the bottom of the hole & mixed in with the spoil will help. Bare in mind that though soils on the coast are typically poor, the shrubs you are using probably also come from coastal regions, and as such do not need rich soils. Over feeding is also likely to produce lots of soft growth that will be hammered by the salty winds. After they are planted they should be watered well & not allowed to get dry until their first winter. Mulching is a good idea as it helps keep weeds down, & therefore competition, & reduces water loss through evaporation around the plant in dry periods. Natural mulches, like composted bark can blow away so artificial ones are usually more practical, they should be water permeable and the edges should secured & buried to prevent fraying. A piece of old carpet cut into 1m2 pieces, slit to the middle & placed around the base of the plant is a good cheap method, there are custom made 'mulch mats' available, these are generally of a dark colour as this raises the immediate soil temperature, so speeding root growth. Some are bio-degradable & will disappear after a few years, by which time they should no longer be needed. Seaweed collected off the shore in March is a fine natural mulch.
Other considerations Often the soil in a coastal garden may be derived from a stabilised sand dune or shingle banks & is exceptionally well drained. In such places it may be desirous to add some organic matter to the planting hole to aid water retention for the plant early on. Having a very sandy is not a great problem though, one of the toughest & quickest shrubs in the wind Olearia traversii from the Chatham Islands will grow happily in even pure sand. However in very friable soils staking of larger shrubs & trees is more important & the regular topping of some vigorous species, as in these more open soils it is easier for them to blow over. Normally staking isn't necessary, where it is drive a stout wooden stake well into the ground diagonally pointing away from the prevailing wind. Attach the stake to the tree or shrub near the base with a proper and appropriate tree tie via a spacer. Ensure that the tie is inspected periodically and loosened as the plant grows and removed after it is no longer required, this will usually be 2 years & rarely be more than 5 years. In a windbreak the shrubs true function is to protect the trees behind them, these will be slower to start & their establishment period longer, which is even more important than that for the shrubs. Remember that trees get big though, don't plant them right next to the shrubby barrier as they will compete & neither will benefit. The planting distance of the trees varies according to the type used. For shelter planting though it is a good idea to plant at half the final distance you want between your trees (what ever tree species you are using the final spacing should never be less than 5m) this will help to fill the gaps between the trees for the first 10 years or so, after which the in-between one should be removed. More over-planting than this will have little benefit & is of little 'insurance' worth as the vast majority of likely losses would be in the first few years of establishment when they can still be easily replaced. If left closely planted they will only spoil the shape of the other trees & make them all less wind-firm.
Conclusion Erecting a hedge or windbreak as you can see takes a lot of work in its preparation & planting, but after the initial effort it needs very little attention & you begin to reap the rewards of all your efforts. A well chosen one should need no watering after a couple of years, no feeding and only a little dead-wooding & pruning. With any shelter planting it is the plants establishment period which is key, if the plant struggles to get going it will take a very long time for it to provide much useful protection. As the windbreak matures you could interplant to brighten it up, a border behind the trees for example with a mixture of shrubs & perennials or plant a few climbers to ramble through. |
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Cytisus ‘Minstead’ & Rhododendron yakushimanum two moderately salt wind tolerant shrubs that can make colourful additions to the inner portions of an established windbreak.
© Garden Cottage Nursery, October 2009 |