The best time to prune coral bark Japanese maple is late fall or early winter when the tree is dormant. You need a pruning saw, lopping shears, bypass pruning shears and, if the tree is tall, a pole pruner.
Prepare your tools
Before you begin, disinfect your pruning equipment in nine parts water to one part bleach to be sure your tools do not spread fungi or other diseases to the tree.
Cut away dead and diseased branches
Any time you notice dead, broken or diseased limbs, cut them away. This does not need to wait until pruning season. Cut broken and dead branches to the tissue ring just above the branch union. Cut diseased branches at least 6 inches below the diseased area, and be sure to disinfect tools immediately afterwards.
Shape the tree
Eliminate crossing or rubbing branches by removing the weaker of the two. To encourage new branches, cut away older, discolored wood. Do not over-thin. Remove no more than one-third of the total branches, and try to space removed branches evenly around the tree. To control the size of the tree, cut branches back to adjoining branches, but try to follow the natural shape of the tree. Cut off no more than one-third of the length of a branch. Keep in mind that the more you trim to control the size, the more you must prune each year as new growth replaces the old.