For many types of trees, summer isn’t an ideal time for major pruning, as the wounds it causes may be exposed longer and “bleed” more prodigiously than in the dormant season, increasing the likelihood of disease or infestation.
That said, there’s definitely a place for trimming trees in the summer, and neglecting it can be detrimental to the tree itself, to surrounding structures, and to human safety.
In some situations, summer’s actually an ideal time for trim work. For one thing, certain hardwoods–including maples, birches, and walnuts–bleed sap extensively during the growing season, and it’s often better to prune these when the year’s new growth has matured and leaves are full-sized. This may be anywhere from late spring to midsummer, depending on the region and the species in question.
Although the peak season for pruning apple trees is usually late winter, summer trimming can also be beneficial: …