Japanese maple trees are easiest to prune during winter or summer, although they can be pruned selectively all year. Winter is ideal because the lack of leaves makes it possible to view the structure of the branches. Summer pruning allows the gardener to determine how much thinning is necessary.
Pruning in the summer gives the gardener more flexibility because plant growth is not stimulated at this time. This means that the pruning results last longer, and the tree's growth does not thicken as much as it does during other seasons.
When the temperature is above 80 degrees Fahrenheit, pruning can cause the tree to be exposed to too much sunlight. This can be harmful because the tree's bark is usually shaded by foliage and is not adequately protected from eventual sun scald.