HEDGES are cheaper than walls and preferable to fences. Where screening is necessary to hide an unpromising outlook, neighbours or buildings, to provide security and privacy or protection from wind, or to create, structure within the garden and provide an element of mystery or surprise, a good hedge is the answer.

A good hedge starts in a good trench. A living barrier may be slow to get started but the whole growing process can be speeded up considerably if sufficient care is given to the planting. The classic method is to dig out - by machine if possible, otherwise by hand - a trench at least one foot deep by one foot in width. The soil in the base of the trench should be broken up to ensure good drainage and a free root run. Ideally the base of the trench will have a layer of well-rotted farm-yard manure or garden compost which will provide nice feeding for the developing young roots of the hedge. The soil which goes back into the trench and which forms a cushion between the layer of manure and the newly planted roots should have a sprinkling of bonemeal mixed into it.

With regard to planting distances, a spacing of 18 inches to two feet between plants will be required and the plants go in a single straight line. Impatient beginners often opt for a double row or a staggered row but that is unnecessary even where a wide hedge is needed.

What to plant? The choice can seem bewildering and here I am thinking of hedges which will reach five or six feet in height rather than little hedges or edgings of box or lavender.

An Irish favourite is beech. It is especially suitable in rural areas as it blends readily with the surroundings. A pleasing feature is the changing foliage colour from the fresh silky green of spring and early summer, to the strong green of high summer, eventually changing to yellow, orange and russet in autumn. Most of the foxy brown leaves are retained on the twigs until early spring.

Beech may seem slow but if well planted and properly cared for it will literally jump out of the ground. Care in the first few years will involve watering and keeping the base weed free. Whitefly, if they attack, should be dealt with, by spraying an insecticide on the hedge. A foliar feed every two weeks during the summer will really help. This regime will repay, with annual growth of up to 18 inches. In three or four years it will make a respectable hedge. From the first year on the sides and the top should be lightly trimmed to encourage bushy growth.

Beech requires reasonably good ground and is particular about drainage. It just will not grow in waterlogged conditions. Hornbeam can make a good alternative to beech where ground is inclined to be too wet in winter.

However, it will not colour as nicely as beech in autumn and it does not carry its brown leaves through winter.

In areas where animals may browse on a boundary hedge hawthorn or holly will be sufficiently animal proof. In general hawthorn is not refined enough for use within the garden and will be better as a stock-proof boundary.

Also thorny and useful as a boundary to keep animal or humans at bay is berberis or pyracantha. Berberis darwinii, pyracantha or holly have - the advantage of being evergreen.

The most usual resort of the new gardener will be the evergreen - and fast growing Leyland cypress. In good and careful hands it will make an excellent hedge and will do so quickly - beech treated as above will be almost as fast growing. The problem with this ubiquitous evergreen is that it can be too speedy and will quickly get out of control unless the gardener is prepared to be vigilant. A well cared for Leyland hedge can look as smart as yew, the real aristocrat of the hedging world.

YEW is on the expensive side and has a reputation for being slow. This is undeserved; a well-planted and cared for yew hedge can reach five feet in six or seven years.

Fortunately no one now plants the evergreen Lonicera nitida with small shiny leaves. It is an ugly nuisance which needs constant attendance. Very regular attention is also required to keep privet looking good. Better than privet is the evergreen griselinia, much favoured for boundaries and quite fast growing. Laurel I consider too coarse for use in the average garden.

By the seaside griselinia will do well as will escalonia but for the most exposed windy and salty areas olearia or the New Zealand daisy bush in one form or another will be the answer. Olearia traversii is the most usual one used as a hedge and it can go up to 20 feet or more in height.