The Katsura tree (Cercidiphyllum japonicium) makes a fairly low maintenance landscape tree, because it has no major pest problems. The tree benefits from annual pruning to control the shape and maintain a strong, healthy tree. If left unpruned, the tree is prone to suckers and wood breakage.
Katsura trees require pruning in part due to the weak nature of the wood. Branches that grow too close to vertical, make a shallow angle with the trunk. These are prone to breakage from the severity of the angle and should be removed. Additionally, major branches should be spaced out on all sides of the trunk to help prevent breakage, recommend United States Forest Service horticulturists Edward F. Gilman and Dennis F. Watson. Katsura trees can also develop suckers along the trunk. These compete with the tree for water and other nutrients and should be removed. Finally, branches can droop as the tree ages, so gardeners will want to trim thee back to relieve the weight and allow pedestrian passage under the tree.
A mature Katsura tree ranges from 40 to 60 feet in height, with a canopy spread of 25 to 60 feet. As a moderate-sized tree, the Katsura should be planted only in sites where it has enough room to mature without being cramped. If your Katsura tree's branches need to be trimmed because they grow too close to the house or hang over the fence, you'll need to do so. Trim long branches back to a Y-intersection or cut them off at the base.
First, identify broken or damaged branches that need to be removed and cut them off at the base. Also cut off any dead wood at its base. Next, clip the suckers from the tree trunk using hand pruners. Remove low-hanging or downward-growing branches to improve movement under the tree. After you've cleaned up the tree, identify weak branches by noting the angle with the trunk and remove these at the base. Lastly, thin out the canopy to increase air circulation.
You will be better able to see the branches of your Katsura tree in the late winter, when the tree is still dormant and hasn't leafed out for the season. Prune at this time. Pruning in the fall can encourage new growth right before winter and should be avoided.