Pruning young black walnut trees will result in high-quality veneer timber. According to Purdue University, pruning black walnut trees may be more of an art form than a straightforward process. The end goal is to create a straight tree trunk that is free of knots and any internal defects. All black walnut trees must be pruned while the tree is dormant and insects are not present. Pruning must take place in the middle of winter.
Select the main central trunk leader of the young black walnut tree. Remove any competing leaders from the tree with the pruning shears. The first selection pruning is generally performed after the first year of full growth from a young sapling. Make cuts back to the main trunk of the tree.
Leave any side lateral branches. Side lateral braches are those limbs that grow from the trunk at a relative 90-degree angle.
Cut all branches that begin to form a “fork” with the main trunk the second year of growth. Use the pruning saw and make the cuts in a two-step process. The first cut should be 6 inches from the main trunk. The second cut must be less than 1/2 inch from the trunk. The wound will naturally heal over.
Prune side lateral branches before they reach 2 inches in diameter after the trunk exceeds 3 to 4 inches in diameter. You can remove up to half of the upper limbs to create a black walnut trunk that is free from defects. In other words, on a 24-foot high black walnut tree the first 12 feet of trunk should be free of all limbs. The growth and size of black walnut trees are fully dependent on the climate and conditions of the timber stand.