Weeping birch is a deciduous tree grown for its green leafy canopy and decorative crenulated, peeling bark. According to the United States Department of Agriculture, any significant pruning of weeping birch should be avoided to limit the sunlight and drying warmth reaching through the canopy to the soil below. Birch trees thrive in moist to wet soil with their roots kept cool, and pruning counteracts these preferences. Pruning that must be conducted to remove damage or prevent interference with nearby structures should be done at a prescribed time during the year. Carefully timed pruning will limit sap weeping and skirt the active period of the bronze birch borer, a killing pest of birch trees.
Prune your weeping birch tree in the period running from the middle of summer to late fall. This timing allows you to avoid excessive sap loss or bleeding that occurs in the spring and the most active period of the bronze borer insect.
Inspect the tree each year for broken branches; diseased, dead or abrading branches; or those that are cracked and may be an entry point for insects or disease. Cut away these damaged tissues, placing all cuts on the bias just outside the slightly swollen branch collar ringing the area where the branch connects to the parent branch or limb.
Restrict pruning for shape and size. If done at all, remove up to, but never more than, a quarter of the live wood in the tree canopy. Reduce the branch length to reduce the spread of the canopy by cutting down the terminal branch tips to the desired length and place the cut on the bias just 1/4 inch above a leaf node or bud.