Silver maple (Acer saccharinum) is the wild child of the maple family. Fast growing and reedy when young, it shoots up to 80 to 100 feet tall with little thought to developing well-formed limbs and protective bark. It is a challenge to prune, and needs trimming almost as soon as it is planted. Without careful pruning, this prolific, moisture-loving giant will block out sunlight in large areas, and its roots can grow into broken pipes and underground tanks, and can even fracture foundation walls.
Prune silver maple only in late winter or very early spring when trees are dormant. Trees pruned when they are growing will take extra time to heal, and the sap that bleeds out of cuts will draw insects and viruses that are not present during winter months. Remove dead wood any time of year.
Reduce crowns annually on fast-growing silver maples. Prune branches by no more than a third, beginning at four or five years of age, to encourage an open, vase-shaped crown. Choose a single, central “leader” for the tree, and remove “suckers” (shoots that spring from the ground alongside the trunk).
Remove branches that grow from the main trunk at a 30-degree or sharper angle; they will compete for water, nutrients and dominance. Remove limbs growing at a 75-degree angle or greater; they are susceptible to wind damage and breakage. Take branches that grow to a diameter more than half as large as the leader as well.
Thin growth along main, sculptural branches to shape silver maple; fast-growing side branches have a tendency to droop, and should be kept clear of driveways, patios and walkways. Remove water shoots (those that grow straight up, close together, along large or “sculptural” branches) and keep twigs and foliage cleaned out to allow good air circulation and light in the center of the tree.
“Cable” old, weakened multitrunk silver maples that were not trained to one leader in their youth. Although this is usually a job for a professional arborist, cabling consists of sinking anchors into both members of a weak “crotch” (juncture of branches) about two-thirds of the distance between the split and the ends of the branches. Anchors are then joined by bars or cables to strengthen the crotch so it can resist breakage. Large cabled branches are also often braced with bolts.