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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 make up 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).
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)
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.
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.
Finally windbreaks should be erected perpendicular to the prevailing wind (SW for most) 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.
Once a windbreak is established the difference inside is quite startling, the micro-climate created is mild & humid. With a bit of shade luxuriant
growth can be obtained with mosses & ferns, spectacular plants such as the the Himalayan blue poppy, Meconopsis ‘Lingholm & Trillium
grandiflorum can be grown. Many plants that don't seem obvious can used to make excellent hedges or windbreak components, New Zealand
flax, Phormium tenax (right) is particularly impressive as a hedge & is useful in a wet soil where it makes a thick barrier to the wind.
Your windbreak is also part of the garden, & should ideally have some aesthetic merit in it's own right.
Here Escallonia ‘Edinensis’, Olearia cheesmanii & Hebe John Collier show that they can do more than just stop wind.
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.
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
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
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
'Yak' hybrids though slow growing are also 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
Olearia macrodonta,
tough quick & attractive
it is an invaluable plant
for the coastal garden
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
Hedges
Plants To Use In Hedges & Windbreaks
Two sample layouts for a 3 layered windbreak in an exposed site.
Fig. 4. On the left, 1st a fence with windbreak netting to aid establishment, then 2 offset rows of vigorous tough shrubs & a row of hardy pine trees
or similar to grow up behind the shrubs & provide long term high level shelter.
Fig. 5. On the right the same tough 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.
If space allows in a very windy site plant a-la Fig. 4 with a single row of lower shrubs 1.5-2m back from row of trees. Two years in this should
allow you to plant a flower border behind these innermost row.
Fig. 6. 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. The 1m spacing is appropriate for
many common coastal hedging varieties types such Olearia,
Escallonia & Fuchsia that have been pot grown up to 2-3L
size & as such are big enough to look after themselves.
Olearia traversii, a quick
growing & very tough large
upright shrub with leaves
glossy green above & shiny
silver below. A 1st rate hedging
plant in sandy soil.
Fig. 7. A 'Cornish Hedge'.
Common in that county, is a
stout earth filled dyke with
tough shrubs planted on top.
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.
Drainage
Types Of Plant
Ensure that your chosen site doesn't turn in to a bog every time it rains. There are plants which will tolerate water-logging 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.
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, 2L or 3L 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 so extra protection will be needed for the new plants.
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.
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 Fig. 6) 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 (not potting compost from a bag, that is different stuff) will help. If these are unavailable a small
handful of Fish, Blood & 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
biodegradable & will disappear after a few years, by which time they should no longer be needed. Seaweed brought up by the winter storms
& collected off the shore in March is a fine natural mulch that mostly stays in place & feeds as it rots away.
How To Plant
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.
Other Considerations
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 inter-plant 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.
Conclusion
Cytisus ‘Minstead’ & Rhododendron yakushimanum two moderately salt wind tolerant shrubs that can make colourful additions to the inner
portions of an established windbreak.
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 Deer posts
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.