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April's issue of The Irish Garden








Trees and Shrubs : Hedges and Shelter belts

Planting |  Spacing | Formal training | Clipping | Informal hedges | Overgrown hedges | Shelter Belts | Planting | Spacing | After planting care of trees

Planting 

A hedge, or screen, is simply a line of trees or shrubs planted close together and trimmed to shape. Apart from providing shelter, privacy and boundaries, hedges can be used as a backdrop for the shape and colour of ornamental plants. A disadvantage is their tendency to draw moisture and nutrients from the surrounding soil. They cast shade too, and they often provide a haven for slugs and snails.

Small hedges can be very decorative

Small hedges can be very decorative

Spacing

Hedges planted at close spacing thicken up more quickly, but cost a bit more. Competition between the plants at closer spacing means they are more easily kept to the desired size. Most common hedges, including evergreens, are best planted 60 centimetres apart. Smaller types, such as berberis and hawthorn, should be planted at 40 centimetres apart.

Formal training

For a formal hedge, training should begin at planting, when the top 15 centimetres of the leading shoots are removed, which encourages the plants bush out lower down. Continue this tipping-back during the first two seasons and shorten strong side-shoots at the front and back of the hedge to keep the hedge narrow and encourage the plants to meet earlier.

Start clipping the sides first, to prevent the hedge becoming too wide. Clip the hedge to a wedge shape to let light get at the lower part. Otherwise the foliage dies and the bottom of the hedge goes bare.

Clipping

Regular clipping follows on the initial training period. Begin regular clipping before a hedge has reached its desired final size. Never let a hedge get beyond its ideal height and then, too late, try to bring it under control, particularly with cypresses. Stop the plants 30 centimetres short of the ideal height and let them reach it over five or six years, thickening up in the process.

Clip hedges to be narrower at the top

Clip hedges to be narrower at the top

The amount of clipping depends on the vigour of the hedge. Privet and lonicera need four or five clippings each year. Griselinia needs two, in May and August. Most others need only one. Late July is a good month – most of the season’s growth being over, but the shoots have not yet turned woody and hard.

Informal hedges

For an informal hedge, such as forsythia or escallonia, and for tall screens, simply let the plants develop naturally for a couple of years. Then trim the sides with a secateurs, shortening all strong side-shoots. Flowering hedges should get this treatment after flowering. Avoid using hedge-clippers on informal hedges or screens if they are to have a natural informal appearance.

Another kind of informal hedge can be clipped to shape. In this case, the shape is informal, not the growth of the hedge. Unusual ‘cloud’ shapes, for instance, can be clipped into a hedge, even one that was formal to start with.

Overgrown hedges

Badly overgrown hedges can be cut back part-way, even right back close to the ground, and they will sprout again. Hedges that have become too broad can have one side cut off. The second side can be cut off, two years later, if desired. April is the month for these operations.

Cypress hedges cannot be cut back in this way, as they do not regenerate from bare wood. Never cut them back beyond the green part of the shoots or they will stay bare.

Shelter Belts

A good large-scale mixed shelter belt

A good large-scale mixed shelter belt

Shelter belts fulfill the same functions as hedges or screens, but on a larger scale. Very many large gardens, rural houses and farmyards would benefit from more shelter planting. Trees can be planted in blocks in corners or in a narrow belt.

Planting

The best shelter belts are porous enough to allow the wind through, but reduce its speed. Dense conifers are better mixed with deciduous trees because mixed shelter belts are better to look at, especially in winter when coniferous shelter can be depressingly dull.

Plant shelter belts across the direction of the wind that is to be slowed down, which is not always the prevailing wind direction. Where possible, plant two or more lines in a shelter belt, mixing at random a number of types such as hazel, hawthorn, holly, poplar, alder, pine, spruce, cypress, beech, larch and birch, choosing size and type as appropriate to the space available and the soil.

Spacing

In single rows, plant shelter trees about 1.5 metres apart. Space double rows about 1.2 metres apart and plant the trees about 2 metres apart in the rows. For multiple rows, space the rows about 1.5 metres apart and the trees 2.5 to 3 metres apart in the rows. Stagger the trees in each row.

Randomise the spacing of the trees in the rows and between the rows to achieve a more natural appearance. This is especially important when planting garden woodland blocks. The finished wood will look much more natural if the trees are not in exact rows.

Garden woodland of birch

Garden woodland of birch

Choosing trees

Choose deciduous native trees and Scots pine, which is given native status by some experts. Good trees for garden planting or close to house and buildings are the smaller ones, such as birch, hazel, holly and hawthorn. For damp ground, use willow and alder. Further from the house, the larger trees, such as oak and ash, can be used. Beech is not native but widely naturalized and Norway maple makes a fine tree for autumn colour. Sycamore is not native but very wind-resistant as is Scots pine and Monterey pine Wild cherry is a fine tree to include in small numbers for its fine spring flowering and rowan for autumn berries. Hornbeam is another non-native that is naturalized in places and very good on heavy land, where beech does badly. Small transplants of these species can be bought in forest nurseries.

After planting care of trees

Fence off shelter belts against grazing livestock, keeping trees at least 1.5 metres from the fence. Keep grass and weeds down for a few seasons with Roundup or similar. Give a little general fertiliser in the early years. If shelter becomes bare at the base as it gets older, try underplanting with common laurel.

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