Prune maple trees as late in the spring as possible, but before the growing season starts in earnest. Pruning too early in the season causes the tree to bleed more sap. To encourage the growth of larger branches, prune away small branches that are sapping energy from the tree. Do not prune more than 15 percent of it in any given year to avoid damaging the tree's long term growth.
Make sure that the pruning implement is sharp enough to make clean cuts, as these heal more quickly and look nicer. Cutting at an angle as near to the trunk or remaining branch as possible aids in recovery. Sterilize the shears between uses to avoid spreading disease and fungus between plants. Be careful not to over prune the tree, as that can weaken it and it may take years for the tree to fully recover. Focus on pruning dead branches or branches that threaten to become entangled with each other or surrounding structures, such as power lines.
While the tree may leak sap from its wounds, these heal and should not be considered a problem. Some experts suggest painting over open wounds to more quickly seal them and prevent diseases or pests from entering the tree. However, other horticulturalists believe that the maple tree can reliably seal and repair its own wounds without an artificial bandage.