When you prune, you’re not just changing the shape of the plant. You’re also influencing what it invests its energy in: more leaves and shoots, or flowers and fruit.
Pruning a fruit tree in winter, when it has withdrawn its energy, encourages strong vegetative growth. This is useful when shaping young trees, or when you want to kick-start growth in an old tree that has become weak. However, pruning too hard can result in a flush of vigorous water shoots.
During summer, the buds that will become next year’s flowers and leaves are formed. You can prune the current season’s shoots in late summer, leaving only a few buds behind. This encourages the tree to invest more energy into those buds rather than continued shoot growth, which promotes the formation of more flower buds and, in turn, better fruiting.