Black walnut trees are grown primarily for their lumber. When pruning, the goal is to choose one branch to be the central leader, or trunk, and remove all side branches up to a height of 20 to 30 feet. Do this over several years, removing the lower-growing branches until the bottom of the canopy reaches the desired height.
Remove all branches that appear dead, diseased or damaged. Cut them off near the main trunk, leaving approximately a ½-inch stump. Do not angle the cut. Do not apply sealant to the cut.
Choose an upright growing branch to be the central leader. It is this branch that will become the trunk of the tree and from which all side branches will grow.
Remove all branches at the top of the tree that are growing near the central leader. Cut them off leaving an approximately ½-inch stump.
Prune out all lower branches that are less than ½-inch in diameter.
Remove any suckers growing from the ground at the base of the tree.