Winter is the traditional time of year to prune apple and pear trees. The reasons for this are partly historical. January and February were quieter months in the agricultural calendar when farm labourers were available to work in the orchards.
In fact, pruning can be done in summer and winter.
As a general rule winter pruning promotes vegetative growth; summer pruning slows growth and encourages fruit production.
Pruning has two main functions depending on the age of the tree:
- On young trees, to encourage a strong branch framework that will support the fruit.
- On mature trees, to maintain its shape and encourage fruit production.
In autumn when the leaves have fallen the tree stores its energy supply in the main trunk and root system. If pruned hard in winter, the tree’s potential for re-growth remains unaffected. In fact, the tree has sufficient energy to support the growth of a much larger tree – the tree it was prior to pruning. Come the spring this will result in vigorous new growth.
With young trees, where the aim is to encourage strong framework branches, this new growth can be shaped to develop a balanced branch system.
However, when a tree responds vigorously it can also result in excessive upright growth on the main branches. These are called water shoots. They don’t produce fruit and can cause overcrowding, so they should be removed in the summer not the following winter. Pruning in winter would only exacerbate the problem by encouraging more upward growth.
Timing is important with winter pruning. It should be done when the coldest part of the year has passed when the tree is still dormant.
Summer pruning stimulates the tree to produce more fruit-bearing spurs. [ Note: This only applies to spur-bearing and not tip-bearing trees] Pruning back to a fruit bud will encourage the tree to concentrate on producing fruit rather than vegetative growth.
Cordons, fans and espaliers should only be pruned in the summer. Once the desired shape is achieved, the objective is to produce fruit not new growth. Pruning in summer will encourage fruit bud formation.
Soft fruit trees such as plums, cherries and stone fruit, should only be pruned in the summer after the tree has fruited but before the end of August. Pruning in the winter can lead to silver leaf, notably in plums. Silver leaf is a fungal disease that can eventually cause the branch to die.
So to recap: winter pruning promotes vegetative growth; summer pruning slows growth and encourages fruit production.