When a tree has outgrown its space in the garden it will need to be reduced in size. It is better to do this sooner rather than later as the longer it is left, the harder it is to prune and less likely it is to recover.
Trees also might need to be pruned and therefore reduced in size if they have dead, diseased, or have crossing or torn branches which can lead to infection.
It is usually best to try and keep tree (and shrub) growth under control with regular pruning however this is not always practical, especially if you inherit overgrown trees and shrubs in a new garden.
When to reduce trees
Many trees are best pruned in late summer when healing is most rapid: Magnolias and Walnuts for example. Prunus (Cherry) trees are best pruned in mid-summer or winter to reduce the risk of Silver Leaf disease.
For most other deciduous trees winter pruning is the correct time when the trees are in their dormant stage and is best accomplished before March as later pruning can result in bleeding.
How to reduce tree size
Depending on the tree involved and the intended effect there are several tree pruning strategies. They are listed here from those requiring the least work, to the most work.
An all over trim in spring or summer: Appropriate for some smaller formal trees, especially evergreens. This will need to be done every year or two. For these smaller trees a long-handled hedge trimmer is a labour-saving option.
Pruning when dormant: Usually involves shortening side-branches all over the tree, making it smaller and more attractive. It lets in light, reduces the tree’s vulnerability to wind damage and is an opportunity to remove diseased or damaged wood.
Pollarding: In this extreme form of pruning, the entire head or crown is removed. This results in attractive small trees, although at the price of repeated pruning.
Crown lifting: Lifting the crown by removing lower branches to increase sunlight in a garden is great value for money when it comes to bigger trees. This is less time consuming than a full reduction of the crown.
Crown thinning: Thinning crowns to let in more light by removing some, usually up to 30 percent, of the branches and concentrating on dead or congested shoots.
Below is a list of problems that can occur if you employ an uncertified tree worker instead of a qualified tree surgeon.
A very common error is to give an all over trim without regard to cutting side-branches. This results in vigorous tufts of unsightly 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. Many trees are also left with a ‘flat top’ to the crown.
If too much material is removed in one year overly vigorous growth can result. It can also affect the health of a tree and risk future fruit crops if carried out on fruit trees.
Coral Spot may appear on stubs of badly cut branches.
The Royal Horticultural Society no longer recommend pruning or wound paints in most cases as they appear to inhibit healing and may actually encourage rot. To encourage healing we make pruning cuts through the branch ‘collar’ (the slight swelling where the branch joins the trunk) as this is where natural healing most readily takes place.