IS IT POSSIBLE TO RESTORE AN OLD OVERGROWN HEDGE?

A well maintained hedge can last for centuries. Indeed old boundary hedges in Britain may be over a thousand years old. But modern garden hedges are often created from a range of exotic plants and may not look good when they get old. They become too thick, gappy, full of weeds or diseased and you may be faced with the options of removing them or trying to restore them to a more useful and attractive state. So just what kind of restoration is possible.

For most conifers the possibilites are limited. When old they are usually green on the outside but the inside of them is brown, old wood. With the exception of Yew these old conifers will not re-grow if you cut back into the brown branches. They will remain brown and an eyesore. Yew however is capable of growing from brown, unpromising wood although decent regrowth may take a year or two. To restore such a Yew Hedge it is recommended to undertake the job over a couple of years cutting back one side at a time. The best time to undertake this is in spring when evergreens tend to be less active. Start near the base on one side of the hedge and move upwards cutting inside the desired final shape to allow the hedge to grow to its final shape. After this pruning the hedge should be given a dressing of general fertiliser and a mulch of organic matter to help it to recover from the works. There is no point in attempting this with a Leyland Cypress or other conifer as new shoots will not grow from the old brown wood that severe cutting will expose.

There are many other evergreen hedges which can take quite severe pruning. For instance Escallonia, Holly, Laurel and Privet can recover from fairly severe pruning in mid to late spring. They will also benefit from a feed and mulch to encourage regrowth. When reshaping remember it is normal to create hedges, especially evergreens, which are a little wider at the top than the bottom. This allows extra light to the base of the hedge which is usually more often in shadow.

Deciduous hedging plants such as the traditional Hawthorn, Beech or Blackthorn can take very severe reduction. Indeed the classic way of keeping farm boundaries as effective barriers to cattle and sheep is to lay them during the winter. This involves cutting deep into the main shoots of the plants near their bases and bending them over. They will regrow as a denser hedge than before they were cut. This is rarely appropriate for garden hedges however where a visual and practical barrier is normally needed throughout the year. It is worth noting that these plants will take any amount of reduction even down to ground level if needed. The general principle is to reduce the height and width of the old hedge to a foot or two inside the desired final height and width. The regrowth can then be trimmed each year to the shape needed

Hedges thrive on annual or more frequent clipping. This keeps the individual shoots and branches dividing from their bases instead of their ends. The result is a denser hedge restricted to the shape you want. If you leave the hedge for a year or two between cuts it will soon become a row of individual plants instead of a dense, well knitted hedge. 

WHICH IS THE BEST WAY AND THE BEST TIME TO CUT MY HEDGE?TO

There are two main reasons to keep a hedge trimmed – to make it look attractive and to make sure it grows dense. If you plant hedging plants and then leave them to grow without regular clipping you are likely to get a very leggy hedge with light between the individual plants. Left long enough, like a farm hedge that has not been cut for years, it will eventually stop being a hedge and become a row of taller trees and smaller shrubs. As such it is not likely to act as an effective physical or visual barrier.

There are several methods of trimming hedges depending on the plant varieties used. For newly planted hedges some species such as blackthorn, hawthorn and privet can be reduced to around 10cm immediately after planting. This helps to ensure that they will branch from low down and make thick hedges. Most other deciduous plants are best reduced by around a third in the autumn after planting. To keep a hedge growing densely the main leaders of deciduous plants can be cut back in the following years and side shoots shortened a little. The principle is to make the shoots on the plants divide frequently to give dense growth and this is best done by frequent trimming. In general the more frequent the trimming the denser and more formal the hedge. Once a hedge has reached the size you want the trick is to cut new shoots just outside the basic framework of the hedge allowing a small amount of new growth to be retained.

Conifers are not normally pruned until they have reached the height of the desired hedge. They can then be trimmed several times each growing season if you have the time and patience. Along with privet and lonicera nitida (shrubby honeysuckle) leyland cypress develop their best form if clipped in late spring, midsummer and autumn. Some other evergreeens such as box, lawson cypress, holly and yew do best with a midsummer and autumn cut whereas Cherry Laurel, Oleaster and Lavender should be pruned once in the autumn.

There are other details to keep in mind. If you want the leaves on your beech or hornbeam hedge to stay on though the winter, which many people do to maintain the visual barrier, they should be pruned in late summer. Hedges of laurel, holly or other broad leaved evergreen plants should ideally be cut with secateurs. If they are cut with shears you will produce unattractive brown edges on the cut leaves. Tall formal hedges should also be cut to be a little wider at the bottom than the top. This stops the bottom becoming brown, adds to the stability of the hedge (some tall hedges such as lonicera nitida have a habit of starting to lean when they are more than about 1.5m high) and reduces the likelihood of snow pulling the hedge apart.

There are many other details to maintaining a good hedge. I would recommend the RHS booklet called simply “Hedges” by Michael Pollock ( ISBN 0 7513 47280) as a very good introduction to the subject.