A weeping willow's natural shape forms a beautiful leafy screen in wet areas and near the borders of yards. As a centerpiece, the tree becomes more troublesome. Low-hanging foliage interferes with mowing, and the deep shade beneath the tree kills all but the most tolerant plants. Willow wood also breaks easily. Early shaping and trimming during the season overcomes most problems with this tree.
Prune young weeping willow trees in late winter to encourage a strong growth habit. Weeping willow naturally grows wide and spreads with many arching branches and multiple trunks. Since the wood is weak, breaking and splitting damages the tree at the weakest points---V-shaped crotches where limbs and trunk fork. Select a central stem for the tree's leader and use limb loppers to remove any competing vertical growth.
Allow the strong horizontal branches to grow. The natural shape of the branch will be up and then out in a gradual arch, but the branches with the most horizontal junction to the trunk will be the least likely to split away under a heavy load of ice or snow. As the tree gains height, lower branches naturally die back and should be cut away at the branch collar. Continue to favor a central trunk with strong side branches as long as the top of the tree remains low enough to reach. A ladder and pole saw help with taller trees. Mature trees with a strong fundamental structure don't require further training.
Prune storm-damaged limbs in summer by using a limb lopper or pruning saw to remove the branch below the break. In winter examine the tree for dead wood and cut dead limbs back to just above the living tissue. Broken limbs often sprout clusters of new branches. Select the strongest and trim the rest back to the main branch.
Prune low-hanging weeping willow foliage only if access to the area beneath the tree is needed. To create access for mowing, use hedge clippers to trim hanging limbs at just above head height. As twigs are cut, branches will lift, changing the shape of the tree's skirt. Spot-cutting around the perimeter of the tree's canopy and then trimming the in-between spaces shapes the tree more evenly than one circling pass. Willows recover quickly, and trimming will be necessary several times during the summer.
Rake all trimmings carefully from the yard beneath the tree and haul them away for composting or disposal. Since willows grow on wet ground, be careful not to damage grass or ornamental plants growing beneath the tree. Companion plantings already under stress from shade and damp conditions can be easily uprooted and killed. Leaving trimmings on the ground quickly suffocates any grass that survives.