We tend to think of pruning as a winter chore best done when plants are dormant. However, there are quite a few plants that benefit from summer pruning. For some, it's a necessity requiring a major effort; for others, it's more of a maintenance task.
Olives, oleanders, apricots and cherries should receive their major annual pruning in summer during the dry season. That's because winter and spring rains can carry disease pathogens into open cuts.
Olive knot and oleander gall are caused by rain or water-carried bacteria that enter into the plant tissue through pruning cuts and bark cracks.
These diseases cause twig dieback and also create knots or galls (small, bumpy, warty-looking masses) that form on branches and twigs.
If you're removing the knots or galls during summer pruning on olives and oleanders, make sure to disinfect pruning tools between each cut with a 1-to-10 mixture of water and household bleach.
Eutypa dieback on apricots and cherries is caused by a fungus. Branches and twigs on affected trees will die back suddenly in summer, with the leaves still attached. The bark will turn darker brown and the interior tissue will be amber colored. Prune apricots and cherries in summer after harvest.
On affected branches, make pruning cuts at least one foot below discolored wood. And while you're at it, prune out any vigorous, straight-up new shoots.
Ortho's "All About Pruning" has good basic instructions and diagrams for pruning apricots and cherries.
Groundcovers including trailing lantana, periwinkle and verbenas will continue to flower longer during the growing season if pruned or sheared back lightly in summer. Cut back each lantana plant to about 10 to 12 inches high. You can use a weed whacker to shear back periwinkle or Vinca minor to about 6 to 8 inches and to remove dead flower heads on verbenas.
Euryops (an ornamental bush with yellow, daisy-like flowers) as well as lavenders are shaped in summer. Use pruning shears to remove dead flower spikes on lavender and to reshape euryops, being careful not to cut into woody tissue on either plant. Cutting into the woody branches will deform the plant's shape, reduce flowering and in extreme cases can kill the plant.
Hedges grow rapidly in summer. Heavy shearing of hedges that removes too many of the outer leaves exposes the interior wood and tender leaves to our scorching summer sun. Sunburn then kills the wood and leaves, resulting in a half-dead, scraggly hedge. Shear hedges lightly and frequently in summer.