Most pruning for apple trees is done during the winter months and before new growth is produced in the spring. However, additional summer pruning can be an effective way to manage young apple trees when used appropriately. It is used primarily to control unwanted growth and to establish a central leader tree structure for apple trees during year of planting and the subsequent two years. Summer pruning involves pinching off young, competing lateral shoots in the upper portion of the central leader (Figure 1). The removal of these competing shoots directs growth into a single shoot and keeps the leader dominant. With a dominant central leader, the desired narrow pyramidal shape of the tree is maintained and shading in the lower portion of the canopy is minimized. This type of summer pruning can be done in late June and July after the potential for fire blight infection is past. If pruning is done too early, fire blight can be spread by pruning.
For mature trees, summer pruning can be used to reduce the height of a tree, and allows more light into the canopy to improve fruit color. With the reduced leaf area, trees produce less root growth than those not summer-pruned. Thus, summer pruning mature apple trees should be done after terminal bud set. If pruned earlier, multiple shoots may be produced near the cuts. It is only recommended in late July for early-maturing cultivars (Gala, Liberty, Jonathan, Red Delicious) or four weeks before harvest for late-maturing cultivars (Red Fuji, Winesap, York, Granny Smith). There are also adverse affects of summer pruning mature apple trees. As shoots are removed from trees, there is a reduction in fruit yield and sugar content in the apples. Also, if excessive wood is removed early in the summer, flower bud initiation for next year’s crop can be delayed or inhibited.
Summer pruning cannot remedy excessive crowding and should not be substituted for planting trees at correct spacing. Crowded, excessively pruned trees will never reach their full yield potential and will have poor quality fruit. However, summer pruning during the first three years after planting is a useful tool in developing a strong tree structure and maintaining productivity.
REVISED: September 30, 2015