This six-year-old silver maple needs pruning to help contain its fast growth.
image by DRW & Associates Inc
The silver maple (acer saccarinum) is a fast-growing, hardy tree that can grow as tall as 100 feet. It transplants easily and grows most rapidly in a moist area, often in wet areas where nothing else, save a willow, will grow. It tolerates pollution well, making it a favorite urban tree. It does have a few drawbacks, though; it can be invasive and often grows roots along the surface, making mowing around the tree difficult. It is also a fairly weak-wooded tree, so keeping it in shape by pruning correctly helps to avoid breakage and wind damage.
Prune maples during their dormant period when you can see their shape and branches. Pruning in late fall or early winter removes wood when pests and diseases are not likely to thrive on the green wood. Remove dead branches any time they are identified. The U.S. Forest Service recommends that you prune "first for safety, next for health, then for aesthetics". Silver maple branches that hang over buildings or sidewalks are safety hazards because the wood is so weak. The trees also send out branches that overgrow the basic shape of the tree.
Trim a maple sapling as soon as it begins to look "weedy". Silver maples should have only one trunk and many grow several. Cut the extra trunks close to the main shoot just beyond the thick branch bark ridge that runs parallel to the branch and thick "collar" that surrounds the branch. Make first cuts on the underside of large branches a few inches out from the collar, then make a second cut all the way through the branch adjacent to the collar. Making a "starter" cut keeps the branch from falling, shredding the bark---and collar that will form the "wound-wood"---as it goes.
Remove branches that form too sharp an angle. These "Y" notches will produce growth that fills in the center of the tree, blocking light and air. The collars often fold back, too, exposing the tree rather than growing together to protect it. Growth from these branches may also grow against other branches, wearing down the relatively thin bark of the silver maple. Trim the ends of branches with "U"-shaped joints to lessen the weight on them.
Prune frequently---yearly if possible. Silver maples need discipline to avoid becoming 100-foot top-heavy monsters. Remove silver maple branches that become thicker than one-half the diameter of the trunk.
Remove branches of less than 2-inch diameter on older trees and remove crowded or intersecting branches to "lower" the crown. "Raise" the crown by removing lower branches to improve air flow and allow more sunlight around the tree's trunk.