Home Guides states that a weeping willow tree requires regular trimming to maintain the shape and health of the tree. To trim a weeping willow, remove all dead or diseased branches by cutting at the wider part of the branch, or branch collar.
Disinfect the pruning equipment after removing any diseased branches. Use one part bleach to 10 parts water. Trim any branches that have been damaged by storms. Remove any sucker growth at the bottom of the tree. This will remove excess stress on the tree. In the winter, remove any branches that are crisscrossing or overlapping any other branches. Trim excessive branches; trim the bottoms of the branches that hang low to the ground. Do this at varying lengths to ensure a good appearance. If the tree looks overly crowded in the interior near the trunk, do more trimming in that area to balance out the density of the branches. It is important to only prune young willow trees in the fall or late winter. If pruning is done at another time of year, the willow tree could have stunted growth. Additionally, do not trim or cut off branches that arch upward. They will naturally flow downward later.
Disinfect the pruning tools
Start out by disinfecting the pruning tools to prevent spreading disease to your weeping willow tree. If you trim off any diseased branches, disinfect the pruning tools to keep from spreading the disease. Use a 10 percent bleach solution.
Remove dead and broken foliage
Remove all dead and broken foliage. If you need to remove a dead branch, cut just above the part of the branch that meets the trunk. Some especially thick branches require a saw. If the branch is broken, cut it off just below the break.
Trim the suckers
Remove the suckers which grow at the trunk of the tree. These stress the tree by competing for nutrients.
Shape the branches
Prune the rest of the branches to keep them from growing tangled together, which, in turn, weakens the wood. Cut off the parts of branches that touch the ground. Cut the remaining branches to different lengths to keep it ornamental. Concentrate your pruning on the thick growth at the trunk of the tree, especially if it's overly thick.