Tree Surgery and Pollarding Trees
Dealing with Branches
As with all garden plants, dead, diseased or damaged branches must be removed from trees as soon as they are spotted. Failure to do this can result in further unsightly dieback or even the death of the entire tree. Any branch which crosses and rubs against another when the wind blows should also be removed, since damaged bark can lead to cankers and other forms of decay.
To gain more access under a tree and to allow more sunlight to reach plants growing below it, remove some of the lower branches back to the main trunk or to a large bough. If you wish to reduce the overall weight of the tree’s crown to minimize the chance of storm damage, remove some of the upper branches. This will also reduce the amount of shade cast by the tree.
Remove heavy branches in two pieces, taking the weight off the tip before attempting to make the final cut close to the trunk The most important reason for doing this is to prevent the possibility of the bark tearing away from the main trunk as the branch falls — such a wound will take a long time to heal and may become infected. To reduce further the chance of the bark tearing, make the first cut to all branches on the underside, then saw down into the first cut to complete the job.
There is some controversy regarding the use of wound sealing paints on severed branches. The exposed sapwood will be prone to disease infection until a callus has grown over it and a coating of paint will reduce this risk. But paint can also slow down the rate at which the callus grows.
On balance, it is probably best to coat all cuts larger than 2.5cm (tin) in diameter with a proprietary bituminous wound sealer as soon as possible, preferably within minutes of cutting. Painting a wound of an hour or more in age could seal in air-borne fungalwhich have already settled. On large wounds, it is better to paint just the outer 2.5cm (tin) of the surface to seal the living tissues, leaving the inner dead tissue completely bare.
Household paint can be used to sealcuts, but may not be fully effective, especially in hot weather when the wood expands — unlike bituminous types, these paints aren’t very elastic once dry and soon crack or flake.
Boughs and Trunks
If it is necessary to cut the tree’s main support framework of boughs or trunk, special care must be taken. Such tree surgery may be for cosmetic purposes or to eradicate diseased and insecure wood.
Heartwood at the centre of a trunk or bough can rot before any outward symptoms are evident, and this seriously weakens the tree — it can fall during a gale and damage surrounding property. If large, flattish, fan-shaped fungal growths, known as bracket fungi, appear on the bark this is a sure sign that internal rotting is at an advanced stage and the bough or trunk must be felled.
Trees often have substantial roots which extend beyond the spread of the top growth. These can cause damage to the foundations of buildings and walls, and to paths andThe larger the root system grows the more vigorous is the top growth, and this may be undesirable in a small garden.
To limit the tree’s development of spreading branches and its ever-increasing height, winter root pruning is a useful practice.
Dig out a trench around the tree, about 1.5m (5ft) from the trunk, putting theto one side. Try not to damage too many small roots with your spade, but aim to expose all the thickest outward-growing roots. Using a pruning saw, sever only the largest roots. It is not necessary to dig up the cut ends, unless they are causing a nuisance.
Finally, refill the trench with the original soil and firm it well. With a large tree it is best to sever the roots on one side of the trunk one year and those on the other side the next year, otherwise growth will be seriously weakened and dieback may occur.
Repeated severe lopping of a tree’s crown, cutting back to the established main trunk or to main branches, is known as pollarding. The effect is to produce a single tight ball of leafy growth at the top of the tall trunk or lots of tufts of fresh growth along a framework of gnarled branches.
Pollarded trees have a unique, almost grotesque appearance and can be used to great effect in a formal garden. This type of tree pruning is also useful where trees are planted close to a building and a broad-spreading crown would occupy too much space. Street trees are frequently pollarded to allow the free passage of traffic beneath their crowns.
Lime trees (Tilia) are favourite subjects for pollarding, since they rapidly regenerate a head of lush green leafy growth after being cut back. Coloured-stemmed varieties of the white willow — Salix alba ‘Britzensis’ (scarlet) and S. alba ‘Vitellina’ (bright yellow) — produce their brightest bark when pollarded annually.