A black walnut tree (Juglans nigra) is grown for its nuts and its wood, which is used to make lumber. Start pruning a black walnut when it is 2 years old to help it develop a good shape and a strong central leader. Begin corrective pruning when the tree reaches 10 to 12 feet tall, reducing knots and keeping the tree from growing into a bush shape. Continue corrective pruning until the tree is at least 17 feet tall. Prune in the dormant season, before new growth appears in spring. Black walnut grows well in U.S. Department of Agriculture plant hardiness zones 4 to 9.
Prune 3 to 4 inches off all developing buds, also called terminal growth, in February or March, but avoid pruning the tree's main trunk, which is called the central leader. Use pruning shears. Repeat the task in July.
Cut back all but one central leader if the tree has two or more central leaders competing with each other. Don't cut back the strongest, healthiest-looking central leader.
Select branches fewer than 2 inches in diameter in the tree's bottom 9 feet if the tree is not grown for lumber or in the bottom 17 feet if the tree is grown for lumber. Use a pruning saw or pole saw to saw one-third of the way into one of those branch's bottom, making the cut about 6 to 12 inches from the central leader. Saw into the top of the branch about 3 inches from the previous cut until the branch falls. Cut back the resulting stub to the branch collar, which is where the branch joins the trunk. Repeat the procedure for the other branches you selected.
Remove all branches from the trunk that have less than a 35-degree angle at the point they connect with the trunk.
Things You Will Need
- Pruning shears
- Pruning saw
- Tape measure
- Ladder (optional)
- Pole saw (optional)
- Work from a ladder or use a pole saw when pruning branches higher than 9 feet.
- Never prune more than 25 percent of the tree yearly.
- Prune dead branches at any time, avoiding cutting into a branch collar.
- The Pruning Answer Book; Lewis Hill and Penelope O'Sullivan
- Purdue University Cooperative Extension: Black Walnut Plantation Management
- University of Missouri Center for Agroforestry: Growing Black Walnut for Nut Production
- Walnut Council: Growing Walnut and Other Fine Hardwoods