PRUNING
The pruning of trees, cutting branches or shoots from a tree, is perhaps the commonest form of tree maintenance. However it’s worth bearing in mind that all pruning involves wounding the tree to a greater or lesser extent; indeed, poorly executed or unnecessary pruning is perhaps the most frequent way in which trees under human management are harmed.
It’s also worth remembering that no tree ever ‘needs’ pruning; it’s only people that need trees to be pruned! Trees have evolved over millions of years, over the vastly greater part of which they’ve managed to muddle along quite well, entirely without the attention of pruning knife, saw or loppers.
Which is not to say that pruning is necessarily a bad thing; well executed pruning may be helpful in adapting the form of a tree to better suit its surroundings, to lessen the likelihood of potentially damaging breakages and, of course, to increase fruit and flower production; in some circumstances it may even prolong the useful life of a tree. But all pruning operations should be carefully considered, balancing the benefits against the potential for harm.
See below for sections on:
REAS0NS TO PRUNE
TREES' RESPONSES TO PRUNING
CONSEQUENCES OF PRUNING
WOUND TREATMENT: to paint or not to paint
TIMING: When to prune & How different species respond to pruning
- Broadleaved Trees
- Conifers
PRUNING TECHNIQUES: Where to cut
PRUNING TECHNIQUES: Some common tree work operations
Reasons to Prune:
There are many reasons why one might wish to cut a tree back but there are perhaps four main ones:
SAFETY - Trees are much less ‘dangerous’ than is often assumed. Nonetheless mature trees close to vulnerable structures or in
well- frequented places, particularly those with public access, may need tree surgery to remove potentially dangerous limbs. Preventative work may sometimes be justified, for instance to reduce wind-loading and lessen the risk of storm damage.ACCESS - Branches overhanging roads, footpaths etc. may need to be cut back or even removed to create adequate clearances; pruning may be advisable to create sensible distances between trees and structures while it may also be necessary to raise the crown of a tree improve access underneath.
SHAPE - Young trees may benefit from formative pruning to ensure a good branch framework develops as it grows; specimen trees may be pruned to when a more balanced and symmetrical form is desired.
PRODUCTION - Orchard trees require specific pruning techniques to promote good fruit production; timber trees may require low branches to be removed to ensure straight-grained, knot-free timber.
The Tree's Responses to Pruning
Anyone undertaking pruning should be aware of some basic plant physiology; in particular, it is important to understand the principal of 'apical dominance'. This is the way that the bud at the tip (or apex) of a growing shoot produces plant hormones, known as 'auxins', that diffuse downwards, suppressing the growth of lateral buds located further down the stem. In this way the plant promotes upward growth and grows to assume a form best adapted to maximise its exposure to light for photosynthesis rather than simply becoming a sprawling mass of bushy shoots.
It also means that when apical dominance is broken, either as a result of damage or due to human intervention through pruning. the result is that lateral growth takes over, creating a bushier or more branched plant. As a result, pruning will often promote growth; taking the top out of a tree with the intention of reducing its visual dominance can often have the opposite result by stimulating it to develop a denser, more wide-spreading form.
It is also important to recognize that any the cutting back or removal of branches from a tree (i.e pruning) is a form of wounding; any action or process that involves damaging or disrupting the protective layer of bark to expose live tissue provides an opportunity for those tissues to be colonized by potentially harmful organisms, notably decay-causing fungi. To reduce the likelihood of harmful infection taking hold, tree’s have developed a natural response to isolate the damaged area. This involves laying down callus tissue which later develops into ‘woundwood’, initially apparent as a roll of new tissue that grows out from the living tissues around the edge of the wound which gradually extends across the cut surface. In healthy, vigorous trees, small diameter pruning wounds may be fully sealed within a few seasons; however larger wounds may take longer to heal and in many cases may fail to do so before decay becomes established. However, once a wound is fully occluded further decay is largely prevented.
Consequences of pruning
It is also important to understand that pruning to remove live branches also removes foliage, thereby reducing a tree’s ability to produce food through photosynthesis; thus one should carefully consider just how much leaf-bearing material will be lost as excessive pruning is likely to lead to stress which, especially in the case of mature trees, may lead to their decline.
A corollary of this is that the tree will try to make good the loss of foliage; poor pruning technique in particular will tend to promote vigorous new growth. It can therefore be misguided to cut back a tree with the expectation that this will reduce shading; while it might initially let more light in, within a short time the dense new growth may well end up causing more intense shading than before.
Similarly, lopping the ends of branches or taking the top out of a tree to lessen the risk of wind damage may turn out to be counterproductive as within a short time the dense regrowth that poor pruning technique promotes may actually increase wind resistance and the risk of breakage. Where some form of crown reduction is required, it is therefore preferable to achieve this through selective thinning, sometimes known as heading back. This involves pruning back leading shoots to a suitable fork and retaining the shorter side branch. This tends to lessen any tendency for the tree to respond with excessive regrowth.
Treatment of pruning wounds: To paint or not to paint?
It was once assumed that, as we apply a sticking plaster or a bandage when we cut ourselves, pruning wounds should also be covered and various ‘wound dressings’ were marketed for this purpose. Research subsequently showed that these dressings were very largely detrimental rather than beneficial. Some slowed or prevented the tree’s own recovery process while others actually promoted decay. There is some evidence that certain treatments can inhibit some ‘fresh wound parasites’, such as the fungus that cause Silver Leaf in fruit trees, but in general the use wound sealants is not necessary and is often detrimental rather than beneficial.
Timing: When to prune?
When it has been decided that pruning is required, a number of factors need to be considered, the first of which is, perhaps, when to carry out the work. Although winter is commonly thought to be the best time and in many cases is quite acceptable, most species will respond best to pruning carried out in the summer months, largely because they’ll be in active growth and will begin the healing process. Some species, such as the plum and cherry and others in the Prunus family are prone to silver-leaf disease and other problems if pruned other than in the summer months.
Advice on the best time to prune different species of broadleaved trees is given in an Arboricultural Association leaflet,, from which the following table has been adapted. The full A.A. guide can be downloaded from the link at the foot of the table, followed by some guidance on the pruning of conifers..
PRUNING BROADLEAVED TREES:
Pruning Conifers
Most conifers respond poorly to pruning; light trimming may be acceptable but hard pruning should be avoided unless absolutely essential.
It is important to note that many conifers will not produce new growth from old wood, so pruning can leave exposed bare areas. This is notably the case with the conifers commonly used for hedging such as the Lawson and Leyland cypresses. While these species generally have dense green outer foliage, their interiors are brown and bare of green shoots. As a result, over-harsh pruning or trimming that removes the outer green foliage exposes the bare interior, as in the example on the right.
Furthermore, as these species will only regrow from green shoots the exposed bare areas are likely to stay bare and unsightly.
Another evergreen frequently planted in gardens and used for hedging is Thuja plicata, (Western Red Cedar); this is slightly more tolerant of being cut back as it usually retains a few green shoots in its interior and so in time it may recover. Nevertheless, hard pruning is still inadvisable.
Yew is an exception amongst evergreen conifers in that it does generally re-shoot quite well following pruning. Nevertheless, light pruning is to be preferred, especially of yew hedges and shaped or topiarized trees.
Pruning Techniques
Pruning branches: where to cut?
Natural branch breakages, such as may result from storm damage, will usually result in a torn stub being left on the tree and over the last few millennia trees have, in general, survived, stubs and all! Nevertheless it is generally regarded as being preferable (and it’s certainly tidier) to avoid leaving stubs following branch removal.
On the other hand it is distinctly bad practice to remove a branch by trimming it hard back to the trunk to leave a ‘flush cut; this creates a much larger wound that will be much more likely to develop decay and will take longer to heal
Above left: an unsightly stub; Right, an unnecessarily large flush cut.
To create as small a wound as possible without leaving a stub one should aim to make the final pruning cut just beyond the branch collar, a more or less swollen zone near the base of a branch where it joins the trunk to form a strong union. Cutting in to the branch collar should be avoided as to do so will hinder the healing process and increase the risk of decay. It is also important to avoid cutting into the branch bark ridge, an area of raised, often roughened bark that forms at the point where the tissues of the branch and the trunk meet. The bark branch ridge is visible in both of the images above where it can also be seen in the right-hand image that the cut extends into this zone.
In the diagram below the dashed line indicates the best place for the final pruning cut, positioned just beyond the branch collar but without cutting into the branch bark ridge.:
However, if one were to make a single cut down that line, in all likelihood the branch would break before completing the cut, ripping down and damaging the tree. To avoid this the three-cut method should be used when removing a branch of any size, as illustrated in the diagram below. The first cut is made upwards, well beyond the bark collar; the second is made further out, cutting downwards until the branch splits off, but only back to the first cut. The third, final cut trims off the stub back to just beyond the branch collar.
Some common tree work operations
When specifying tree work operations, either to instruct a potential contractor or in cases where the operations require notice to be given to the local planning authority, the following general terms may be of assistance.
