Summer is the time to prune Japanese maples for shape. This is a follow up video to the Winter Pruning of Japanese maples. If you have not seen that video, it would be useful to view it before this video. This Japanese maple had been pruned by Bop over six years to get the basic framework shape. Once the framework is set, it is just a matter of pruning to keep the overall shape.
Deadwood can be taken out at any time throughout the Season, but pruning new growth is done in the Summer. It is very important that maples should not be leaf pruned too late in the Season. Any pruning for shape should be done before Labor Day and is even advisable not to prune past the middle of August unless there is an urgent need to remove growth.
Maples and all trees and shrubs go through a process as the weather cools in the Fall called 'hardening off'. The sugars and nutrients in the leaves begin to move into the roots to support the tree over the Winter. If you prune too late in the Season, new growth will emerge but it will not have enough nutrients and sugars to support the new growth and the leaves will die back. This will stress the tree and may even cause the entire branch to die back if too much growth is removed too late in the Season.
Bop demonstrates the proper pruning techniques on Acer palmatum dissectum 'Inaba Shidare' but this type of pruning applies to all maples.