Quaking aspen is known for smooth white bark that scars black, and heart shaped leaves with fine, saw-toothed markings. These leaves are attached to the tree with a long, flat stem. Because of this, the slightest breeze will cause the leaves to flutter, making the whole tree seem to shiver. It's this distinctive characteristic that gives a quaking aspen it's name. Quaking aspens grow in large colonies with a single root system, and can tolerate any soil. Pruning should only be undertaken to maintain the aspen's shape and health or to remove branches for safety.
Wait until winter to prune your aspen tree. Trees that are pruned in the summer months are more prone to diseases. In winter months, the pruning wound will "scab over" and heal, without leaving the tree open to pests and disease.
Pinch young aspen shoots to shape them early in the growing process. Shaping aspens when they are young may prevent the need for serious pruning later on. Never pinch the topmost branches of an aspen. Topping, tipping or shearing an aspen tree creates an unnatural shape and may cause diseases later in the aspen's life.
Sterilize your pruning saw with methanol to prune an established aspen tree. The recommended method for pruning an aspen is to thin it by cutting branches back to the trunk of a tree. Thinning the tree will help it to maintain shape and improve air circulation through the branches to prevent fungus from growing.
Decide which branches that you will remove with respect to the scarring pattern that you will leave behind, since each branch that is removed from an aspen will leave a black scar on the trunk.
Cut your branches with angular cuts that begin just outside of the bark ridge and angle down and away from the stem of the tree. Avoid injuring the bark ridge or branch collar. Always cut branches cleanly, without tearing.
Remove any diseased branches. Re-sterilize your saw with methanol after cutting each branch to prevent spreading infection.