So there are a few good reasons to prune your deciduous tree.
First off, identify the purpose of pruning your deciduous tree. Resist the urge to prune a shade tree just because your neighbor is pruning their trees. Resist the urge to trim the tree just because is a growing very fast. Whenever you prune a tree there will always be some sort of response from the tree. That’s why the optimal time is in the winter when the tree is focusing on root growth and not sapping as much is it normally does during growing season.
If you trim too much of the tree during the growing season it can have major impact on the health of the tree by cutting back on its food supply since the leaves are catching the sunlight and creating food for the tree. Poor pruning technique can lead to unwanted insect problems, decrease the vigor of the tree, create water sprouts from the base of the tree or within the tree canopy.
The very best time to trim the tree is when the foliage has dropped. Typically the drop occurs between November and December, depending on what region of the country you are in. Pruning should be done before the buds show evidence of swelling in the spring. Winter is the very best time to prune your deciduous trees.