Trees: pruning

This advice is suitable for open-grown ornamental trees. Although pruning does make trees slightly smaller than they would be without pruning, attempting to keep a big tree small by pruning is usually unsuccessful. This advice does not apply to restricted tree forms such as fans and espaliers.

Deciduous trees

Deciduous trees (ones that lose their leaves in winter) are usually pruned in autumn and winter. In some cases, for example with magnolias and walnuts, pruning is best done in late summer, as healing is quicker. 

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

Some trees can bleed sap if pruned in late winter and early spring. Although seldom fatal, this is unsightly and can weaken the tree. Birches and walnuts often bleed if pruned at the wrong time. Summer pruning can be useful to check over-vigorous growth, for example in suckering species of Populus, or restricted forms of fruit such as espalier apples. This pruning is generally light, and is carried out late enough not to promote new growth. Similarly, healthy trees will generally tolerate minor pruning in the summer months, for example, corrective pruning to raise hanging branches, or removing weak growth, which can be easier to assess in full leaf.

Evergreen trees

Evergreens seldom need pruning, although dead and diseased branches can be removed in late summer.

Prior to undertaking any work, it is essential to ascertain if a Tree Preservation Order (TPO) is in place or if the tree is in a Conservation Area. If either is the case, seek permission from your local council before beginning work. Potentially dangerous limbs can, in theory, be removed without permission but the penalties for breaching the legislations, inadvertently or not, can be severe.

Safety is of prime importance when working with trees, so make an honest appraisal of your capabilities, assess the area in which any branches may fall, and erect warning signs or barricades if necessary before beginning. If in any doubt engage a professionally qualified tree surgeon or aboriculturist.

Take a step back and decide what needs to be done to produce a balanced, attractive tree. Work with the natural habit of the tree to shorten or remove branches. Going against the tree’s natural habit produces ungainly trees that lack grace.

Always start by removing damaged, dead, diseased shoots, followed by weak, lax or rubbing growth.

When pruning out disease, clean you pruning tools with disinfectant between cuts. Minimise disease spread by pruning in dry weather, bagging up material and disposing. Only stack healthy logs as animal habitats.

How to remove tree branches and limbs

• Wear 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 (¼in) above the bud. Beware cutting too close, as this can induce death of the bud. Beware cutting too far from the bud, as this can result in dieback of the stub, and entry of rots and other infections
• When removing larger limbs, make an undercut first about 20-30cm (8in-1ft) from the trunk, and follow this with an overcut. This will prevent the bark tearing, leaving a clean stub when the branch is severed  
• 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
• There is no need to use wound paints, as they are not thought to contribute to healing or prevent disease. The exception is plums and cherries (Prunus sp), where wound paint may be used to exclude silver leaf disease spores

If pruning cuts bleed sap, don’t bandage or bind the cut, as attempts to stem the bleeding are likely to be unsuccessful and may impede rather than aid healing.

Apart from the problem with sap bleeding from the pruning cuts, silver leaf and coral spot, there are few other problems to contend with.

Coppicing
Fan trained trees: initial training
Fan trained trees: pruning established fans
Pollarding
Pruning for colourful stems or large foliage
Shrubs and trees: light pruning
Trees: formative pruning
Trees: reducing their size safely
Woody waste: shredding and composting
Woody waste: using as a mulch