This section outlines basic pruning of young trees during the establishment phase. Pruning and surgery of large and mature trees should only be carried out by fully trained workers.
Formative pruning
Young trees can be pruned to encourage strong upright growth and reduce side branching. This is important for trees grown for timber, but is not necessary on other trees. The amount of side branching will vary with the species, and with the distance apart which trees are planted. Closely planted trees produce fewer side branches. Trees grown singly in open ground tend to produce a much more branching, rounded shape.
The desire to produce natural looking wooded areas with a variety of tree shape and form needs to be balanced against the requirement to get trees established quickly. Pruning of side branches of most major woodland species including ash, oak, beech, lime, poplar and cherry produces strong upward growth. This has the advantage of quickly getting the leader up out of reach of vandals and deer. It also reduces the length of time when the developing woodland is at the ‘thicket’ stage, which many people find unattractive. In parks and other public access areas thickets are often viewed as ‘overgrown areas’ which tend to have negative associations of attracting unsocial behaviour. On the other hand, low branches and thickets may have practical uses in reducing access and vandalism, and may be desirable for screening, shelter from the wind, and noise reduction.
On balance, the need to establish trees quickly is usually the most important factor in successful woodland establishment, and selective pruning will help. Shrubs and thickets of growth can be encouraged at the edges of the planted area and in places away from public access, where their wildlife value will anyway be higher. Concentrate on getting clear-stemmed trees growing in the most visible areas, within view of paths, roads and other access areas. On sites where the value of tree planting is questioned, a band or clump of clear-stemmed trees will often be seen as enhancing the landscape, whereas an ‘overgrown’ thicket will not.
Pruning as an activity is also useful because it involves looking closely at the trees and encourages other aspects of aftercare. For many voluntary groups the labour intensive nature of pruning is a not a problem.
The best time for pruning oak, ash and cherry is between mid June to mid August, as this reduces the chance of bacterial or fungal infection. In the dormant seasons wounds are slow to heal and susceptible to damage by frost. Other species can be pruned at the same time, or between September and December. Never prune during the early growing season of February to May, when the sap is rising fast. Don’t prune every tree, but choose the strongest growing, most upright ones of each species, leaving others to branch more freely and create structural diversity. leading shoots which have forked due to damage or browsing should be pruned to leave a single leader. Trees which have been heavily browsed by deer and have formed a bushy top should be cut back to the main stem to encourage a single leader to emerge.
Side branches should be removed before they reach 2.5cm (1”) in diameter, using a cut as shown below. To promote very fast growth, for example with ash or cherry, start two to three years after planting and prune away the side branches quite severely, leaving a clear stem about half the height of the tree. The developing crown can be balanced by tip-pruning the strongest branches, except the leader, to inhibit their growth, and severely pruning the weaker branches to stimulate vigorous growth.
Pruning of side branches from the stem can be repeated every other year until the tree is about 10 years old, aiming for a crown of branches about one third the height of the tree. Long-handled pruning saws or treetop pruners will be necessary to reach the side branches. New shoots in the trunk, called epicormics, can be rubbed off or cut away with a sharp knife. In this way it’s quite possible for an ash or cherry to grow to at least 6m (20’) height within 10 years. Pruning should stop when the trunk has a diameter at breast height (dbh) of about 12cm (5”). By selecting and pruning trees in this way you can quickly add diversity to the woodland, and encourage the growth of particular individuals or stands of trees which become ‘feature trees’ within the wood. To encourage the dominance of selected trees, removal of nearby trees may be advisable.
Prune side branches as shown. Don’t cut too close, or you will damage the main stem. On most branches, and particularly those the tree is preparing to shed, the ‘branch collar ’ is visible (see below). Always make the pruning cut to the outside of the branch collar position. On the other hand, don’t leave a ‘coat peg’, where rot can start. Aim to cut the branches at a stage when they can still be cut through with secateurs or pruners, either long-handled or treetop type for high reach. Pruning saws, both pocket size and long handled can also be used. If the branches are too big to be cut this way, you have left it too late.
Cutting larger branches
You may need to cut larger branches which are overhanging paths or tracks, or to remove branches which are unsafe. Branches over about 15cm (6”) diameter should only be cut by trained and experienced people.
Never cut inside the position of the branch collar. On decaying and dead branches this can be clearly seen, where it forms a natural barrier to protect the live tissue as the branch decays. Whether you are pruning live, dying or dead branches, always leave the branch collar intact.
Cut branches over about 25mm (1”) in three stages, as shown. If you try to saw through them with one cut, they are likely to break and pull off a strip of bark, which damages the trees.
Make the first cut about one third of the way through the branch from the bottom, but not so far that the saw binds. Make the second cut as shown, to sever the branch, leaving a projecting stub. Finally trim the stub with a third cut, starting at the top.
Don’t leave a snag or stub. At best, this will only produce a mass of unsightly regrowth. More often, stubs die back, providing a foothold for infection and rot which can then be more easily transmitted to the rest of the tree.
Wound treatment
There is normally no need to treat cuts and wounds in trees with a wound paint, which in the past was recommended for the sealing of wounds against fungal attack. If the tree is healthy and the pruning cuts have been made cleanly and correctly, no further treatment should be necessary. The branch collar forms a protection boundary to prevent the inward spread of pathogens.
Treatment after pruning may be necessary on fruit trees, for example plums, which are prone to infection with silver leaf disease if pruning cuts are left untreated.
