Why do trees need pruning?

TTS Tree Surgery: Why do trees need pruning

Why do trees need pruning?

Good-looking healthy trees in your garden make a great feature. And fruit trees also bring the blessing of annual crops to eat.

But, like many plants, to stay healthy and manageable, they need to be pruned properly.

The benefits of pruning your trees

There are typically two reasons for pruning a tree:

  1. It needs to be reduced in size – as it’s outgrown its current space in your garden. This is best done as soon as possible, as the longer it’s left, the harder it will be to prune it and the less likely it will be to recover.
  2. Disease or damage – trees need to be pruned and reduced in size if they have dead, diseased, crossing or torn branches. Pruning will help the tree survive and mitigate further spreading.

When to prune your tree

It’s usually best to keep tree growth under control with regular pruning. But this isn’t always possible, for example – when you inherit overgrown trees in the garden of a home you’ve just bought.

For annual pruning, many are best pruned in late summer because healing will be most rapid then. Examples are magnolia and walnut trees. In contrast, cherry trees are best pruned in mid-Summer to minimise the risk of silver leaf disease.

Others prone to silver leaf disease, such as Prunus sp, are best pruned from April to July – when the disease spores are not airborne and the sap is rising rather than falling (which pushes out infection rather than drawing it in).

With most other deciduous trees Autumn or Winter pruning is easiest as the branches are more visible. It’s best done before Christmas as later pruning can result in bleeding.

Some trees can bleed sap if pruned in late Winter or early Spring. Although rarely fatal, it’s ugly and can weaken your tree. Birches and walnuts often bleed if pruned at the wrong time.

For most deciduous trees, though, Summer pruning can be useful to check over-vigorous growth. This pruning is generally light and is carried out late enough not to promote new growth.

Similarly, healthy trees usually tolerate minor pruning in the Summer months to raise hanging branches or remove weak growth.

Evergreen trees rarely need pruning, though dead and diseased branches can be removed in late Summer.

Checking if your tree is protected

Before you consider pruning a very large or old tree in a garden you’re new to, check with the tree officer of your local council if there’s a Tree Preservation Order (TPO) to protect it. If so, you’ll need to find out what can be done to maintain its health and are probably best to have a professional do the work. Beware – damaging or cutting down a tree subject to a TPO can result in a fine up to £2,500 or, in some cases, unlimited!


Tree pruning strategies

There are several tree pruning strategies you can use, depending on the type of tree involved and the intended effect you’re going for. They’re listed below in order of how much work they entail.

  • A trim in Spring or Summer: This is only appropriate for some of the smaller more formal types of tree, especially the evergreens. You should trim them every year or two. A long-handled hedge trimmer will save you a lot of time and effort for this.
  • Pruning when the tree is dormant: This technique lets in light and reduces the tree’s vulnerability to wind damage and also gives you the chance to remove diseased or damaged wood. It usually involves shortening side branches all over the tree to make it smaller and more pleasing to the eye. To get a balanced end result, work slowly and carefully and check the effect of removing each branch. Not suitable for trees prone to silver leaf.
  • Pollarding: This is an extreme form of pruning, usually best done by a professional. In it, the entire crown is removed. For guide on doing it, go here on the RHS site.
  • Crown lifting: Pruning out lower branches to lift the crown of your tree will allow you access for mowing, mulching and to enjoy the shade cast by the tree.
  • Crown thinning: This is typically done to let in more light by removing up to 30% of the branches. Another strategy is to concentrate on dead or congested shoots. Think very carefully before going down this route – it’s very easy to spoil the look of the tree doing this, so it’s best done in stages, checking the effect of each one before doing any more.

Tree reduction:  not an exact science

Successful tree reduction requires cutting the tree with the right strategy in the right places at the right time. Get it badly wrong and you could kill your tree, creating to a problem to remove and replace it.

Each type of tree will allow up to a certain percentage of pruning depending on its type, its growth pattern and what time of year it is. Check the RHS website for details of yours, or call us to ask about what times are best used in the northern Scottish climate we live in.


How to prune a small tree

Before you start, put on strong protective gloves and, if necessary, eye and head protection.

When cutting a stem, cut just above a healthy bud, pair of buds or side shoot. Where possible, cut to an outward-facing bud or branch to avoid congestion and rubbing of branches

Make your cut 0.5cm above the bud. Beware cutting too close, as this can cause the death of the bud. Cutting too far from the bud is also bad – it can result in dieback of the stub and entry of rots and other infections.


How to prune larger branches

If you plan to take off a branch it needs to be cut at the right growth point. So when removing larger branches, make an undercut first about 20-30cm from the trunk and follow this with an overcut. This will prevent the bark tearing – leaving a clean stub when the branch is cut off.

Then remove the stub – first making a small undercut just outside the branch collar (the slight swelling where the branch joins the trunk), followed by an overcut to meet the undercut, angling the cut away from the trunk to produce a slope that sheds rain.

Avoid cutting flush to the trunk – as the collar is the tree’s natural protective zone where healing takes place.

Wound paints aren’t necessary as they’re not believed to contribute to healing or prevent disease. The notable exception is plum and cherry trees (Prunus sp), where wound paint may be used to exclude silver leaf disease spores.

If pruning cuts bleed sap, don’t try to bandage or bind the cut, as attempts to stem the bleeding are unlikely to be successful and may make things worse.


Common problems

A very common mistake is to give an all-over trim without proper regard to cutting side-branches. This results in vigorous tufts of ugly regrowth spoiling the shape of the tree. These will later need to be thinned out allowing selected shoots to regrow and restore an attractive shape to the tree.

If too much material is removed in one year, vigorous growth can also result. This often occurs when apple trees are pruned too hard.

Coral spot – a fungal disease of woody plants – may appear on stubs of badly cut branches. It often indicates the plant has been weakened by other factors. Prune out infections promptly in dry weather and cut back to healthy wood. Do not leave dead wood to moulder and generate spores.


When to call for professional help

The RHS advises that if the branches to be removed are larger than the diameter of your wrist or if a lot of work up ladders is necessary, it’s best to call in a professional tree surgeon.

It also advises that pollarding, crown lifting and crown thinning are also all best tackled by a professional.


Get in touch

Get in touch to arrange a free visit and quotation for professional advice on looking after your trees and what we can do using the latest techniques and our professional-grade equipment. Pruning is one of our specialities.