There are 65 varieties of ash trees in North America, ranging from small, slender types that resemble saplings to large, leafy trees. As with any tree, ash trees require pruning for many reasons: to remove dead or damaged branches and to maintain the health of the tree, to keep its desired shape and appearance, and to protect yourself, your neighbours, and any passersby from falling tree limbs.
The First Pruning
An ash tree should receive its first pruning the day you plant it. Using pruning shears, trim off any dead or broken limbs. You can also prune the branches to begin to shape the young tree. Never lop off the top a tree; it ruins the shape of the tree and weakens the branch structure.
Shaping the Tree
As the young tree grows, remove branches that are low on the trunk. In time this will create a tall trunk and a full, bushy crown of leaves. If the branches are 1 inch or less in diameter, prune them with long-handled lopping shears. If the branches are more than 1 inch in diameter, use a hand saw for low branches or a pole saw for high and hard-to-reach branches. Bear in mind, however, that a pole saw is difficult to operate from the ground and probably will not give you the clean, even cut you desire.
The Proper Season
Once your ash tree is established and maturing, the best time to prune it is in late winter when the tree is dormant. Pruning a tree as it begins to put forth new leaves and branches can make it vulnerable to insects and diseases.
Whether they are healthy or not, prune any branches that overhang a house, a parking spot or driveway, or a sidewalk, as well as branches that interfere with power lines, or obscure a traffic signal. If you use a chain saw to prune large branches, wear protective gloves and goggles. Never raise a chain saw above your shoulders or use a chain saw while standing on a ladder; if you lose control of the saw, it could inflict a serious injury.