Storms have become a more familiar feature of our weather pattern in recent years. Whilst severe wind impact can be obvious when it comes to structural damage (remember Ophelia in 2017), more ‘normal’ weather can also be very destructive in gardens, and can cause loss of yield and quality, particularly in specialised crops of top fruit, ornamental trees, hedges, cut flowers and foliage plantations.
Planning for shelterbelts and windbreaks is vital in horticulture, not only to protect infrastructure such as buildings, tunnels etc, but especially in demanding situations where cultivation is not possible without protective plantings. Equally, the value of shelterbelts and windbreaks in relation to carbon capture and biodiversity should not be underestimated.
Much of the guidance below has been drawn from experience while screening species in the development of the cut foliage enterprise in both coastal and inland sites. Here selecting a suitable windbreak, comparing rates of growth and tolerance of salt-laden winds provided valuable insights into a range of species.
PERIMETER PROTECTION
When it comes to perimeter shelter species, Pinus radiata (Monterey pine) and spiny-coned Pinus muricata (bishop pine) are both fast-growing species; however, being natives of California, they are not reliably hardy in all of Ireland.
The hardier two-needled European pines, P. nigra (Austrian pine) and the more conical P. nigra calabrica (Corsician pine), do well in most situations. Though often held to be overdone, x Cupressocyparis leylandii (Leyland cypress) tolerates salt spray and trimming. The parent Cupressus macrocarpa (Monterey cypress) is a well-tested seaside plant, though one of the best is the yellow C. m. ‘Goldcrest’.
Deciduous trees are not generally recommended in coastal sites, largely because their shoot tips are more prone to wind and salt damage, meaning growth is slow and the shape of plantations often dramatically windswept.
Three-row deep perimeter planting is recommended on the most windswept locations. While this is a minimum for major schemes, two rows or even a single row is worthwhile if valued horticultural land cannot be spared. Staking is avoided not only on the grounds of cost, but also because anchorage is firmer from roots wind-tested during development.
MOISTURE LOVERS
Moisture-loving species such as Salix alba (white willow), a graceful tree, provide effective shelter. The willows are both economical and attractive trees but perhaps not where tall belts are required. The bushier types like S. dasycladon and S. viminalis can be considered, with S. caprea (goat willow) holding its own as a shrubby plant on an exposed site.
At Teagasc’s Kildalton College in Piltown, Co Kilkenny, Alnus cordata (Italian alder) – a handsome, fast-growing tree that is easy to propagate and manage – makes an excellent shelter belt. Other suitable alder species include A. glutinosa (common alder), A. incana (grey alder) and A. rubra (red alder).
Successful in windswept situations include some of the Sorbus group. Sorbus aria ‘Lutescens’ (whitebeam) has done well, producing a medium-sized tree with attractive foliage. S. intermedia (Swedish whitebeam) is also satisfactory.
Where rapid growth is not essential, Acer pseudoplatanus (sycamore), Fraxinus excelsior (common ash) and Castanea sativa (sweet chestnut) are suitable choices.
The fast growing Eucalyptus, while being a widely grown cut foliage species, is in itself a very suitable shelterbelt, with E. globulus and E. niphophila being reliably hardy and salt tolerant. Other species such as E. coccifera and E. subcrenulata will form excellent hedges with some judicious pruning management.
If salt wind battering is to be withstood, the New Zealand native daisy bushes such as Olearia macrodonta are most reliable, but O. traversii and Pittosporum crassifolia are worthy of inclusion where hard frost is rare.
Other low-growing evergreens such as Atriplix halimus (tree purslane), Brachyglottis greyii, and Eleagnus macrophylla and ebbengei are bold plants and wind tolerant.
The reliably hardy Prunus laurocerasus (cherry laurel) is particularly suitable for inland sites. In cut foliage plantations, single lines are often left unpruned to allow them to develop as shelterbelts to very good effect, guarding against wind damage to the foliage which could otherwise render the stems unmarketable.
COLOURFUL DEFENCES
For outer defences, Phormium texax (New Zealand flax) is a helpful plant in the most tested seaside garden. The bamboo, Arundianaria japonica A, is similarily useful. Deciduous hedge plants considered reliable include Fushia magellanica, Ligustrum ovalifolium (the common privet, often evergreen in places) and Sambucus nigra (common elder).
Recommended thorn hedging on exposed sites include Hippophae rhamnoides (sea buckthorn) as the best choice, followed by Crategus monogyna (common hawthorn).
PLANTING & SPACING
Because of strong gales, spring planting is generally preferred, but careful provision must be made for the dry period (usually encountered from about mid-May). Close planting produces a dense hedge most quickly and root holding is more secure. Spacing, mostly governed by available funds, may be between 46 cm and 76 cm, although greater distance is reasonable for some deciduous species and more expensive hedge choices.
The distance between lines of all wind barriers should ideally be planned for ten times the ultimate height of the barrier. So a 3 m high hedge may be expected to provide maximum shelter of 30 m to leeward. Experimental work has shown that for the greatest efficiency, a barrier should be about 40 per cent permeable.
In terms of maintenance, two annual clippings are better than one but costs restrict this possibility. Trimming should ideally follow an ‘A’ shaped section.
SENSIBLE MIXES & SUPPORTS
When considering costs and maintenance, there are many situations where low artificial screens such as ParaWeb or Netlon make a better choice for farmers and growers. By planning a sensible mix of artificial and living barriers, the interests of economy, amenity and biodiversity can all be accommodated.
Department of Agriculture, Food and the Marine (DAFM) schemes – such as the commercial horticulture grant scheme – will consider support for living and artificial shelter where it is justified for protection of horticultural structures and as a windbreak for nursery and selected field crops. ✽
Andy Whelton is a specialised advisor in the Teagasc Horticultural Development Department. He has spearheaded the developments in cut foliage as a new sector in commercial horticulture. He also works closely with outdoor vegetable and protected crop businesses in Munster and south Leinster. andy.whelton@teagasc.ie.
