Black walnut (Juglans nigra) can grow to a height of more than 100 feet and live for a century or more. Its nuts are exceptionally hard to crack, and when they fall, encased in a fleshy, green fruit, they can dent steel car roofs. If you wish to prevent a black walnut from producing nuts, there are two methods you can try that don't involve chemical sprays: pruning and fertilizing. The pruning method is most effective when the tree is young.
Clip off blossoms from black walnut twigs when they appear in spring. If blossoms are allowed to pollinate, they will produce fruit. If they're gone, fruit won't develop. Use long-handled pruning shears for lower branches, and pole-handled shears to reach higher into the canopy.
Cut down the other black walnuts on your property, leaving only one. Black walnuts are slightly self-fruitful (wind pollination), but will be much less likely to pollinate if there is only one tree. Fell young trees with a hatchet, directing the fall with your hands. Use a chainsaw for trees with trunk diameters of more than 12 inches.
Apply a nitrogen fertilizer to the soil around the black walnut in early spring and late summer. Water it in well, to make sure the nitrogen soaks the root zone where it will be absorbed. Extra nitrogen causes a flush of vegetative growth while limiting fruit production, according to Washington State University.