Summer pruning is a fairly new practice, often not covered in older pruning guides. It is intended to maintain a shorter, smaller size for deciduous fruit tees to make harvest easier and to open up the center of the tree canopy so that sunlight reaches the fruit and to improve air circulation around the fruit. Good airflow through the interior of crop-producing trees helps prevent diseases and pest insect infestations.
Winter pruning invigorates deciduous trees and encourages young fruit trees to grow at a faster rate; summer pruning slows overly vigorous growth and contains the size of mature trees.
Summer pruning is best done from May until July in several sessions as new unwanted shoots and branches appear and as an overly full canopy of leaves shades the ripening fruit.
Start summer pruning as you would in winter. Sharpen your tools and keep them sharp as you cut. Remove dead and diseased wood and broken branches and any branches that cross through the interior.
Then look for shoots heading the wrong direction, shoots or branches that are attached to the main trunk at less than a 45-degree angle (they are prone to breakage when loaded with fruit), or small new branches that will cross through the interior if left to grow to full size. On young trees, removing the shoots when they are less than 6 inches will not affect the tree’s vigor or next year’s fruit set. On mature fruit trees, removing vigorous shoots that grow straight up will curb or suppress the tree’s energy.
Head back tip growth to control height and thin branches, removing no more than 30% of the foliage during the summer. Leaves make food for trees; removing more than 30% of the leaves with any pruning will severely stress the tree.
The scaffolding or branch structure is more clearly visible in winter when fruit trees are bare of leaves. When pruning in summer, go slowly, remove the most obviously wrongly placed branches first and then take a good look at the scaffolding. You’ll want to keep a balanced branch structure with strongly attached secondary branches evenly spaced around the trunk.
Orthos’ “All About Pruning” guide does not include summer pruning instructions, but it does provide good, clear illustrations for pruning many types of fruit trees. The illustrations show just what a good scaffolding on a fruit tree should look like and how to open the center of the tree to sunlight and air (vase training). The book is available used from many sources online.
The University of California Division of Agriculture and Natural Resources website will bring up several downloadable publications on summer pruning.
Note: Apricots, olives and oleanders should be pruned during the dry summer months. When pruned in winter, rains can carry disease pathogens into fresh pruning cuts. Eutypa dieback, a fungal disease, attacks apricots causing sudden limb death in summer. Dark cankers form on pruning cuts and the cuts ooze a gummy substance. Oleander gall and olive knot (gall) are caused by bacteria which are carried by rain or overhead watering into fresh pruning cuts. The bacterial infection causes round hard galls to form on twigs. The galls can girdle twigs and kill them; on olives even a few galls can affect the taste of the olives.