See also: Walnuts
Black Walnut trees (Juglans nigra) are native to North America. Their edible nuts have an extremely hard shell, so black walnuts are not as popular as the English walnut of commerce.
The trees may grow to 150 feet tall and live up to 250 years. More typical is 75 to 100 feet in height and 150 years. They are mainly valued for their fine grained wood especially in the furniture industry.
Black walnut trees secrete 'juglone', which kills many herbaceous plants around the root system of the tree. It's own natural weed killer!
Plants adversely affected by being grown near black walnut trees exhibit symptoms such as yellowing and wilting of foliage, and eventual death.
Juglone is a respiration inhibitor which deprives sensitive plants of needed energy for metabolic activity. It is released by live roots and accumulates under the canopy of the tree from decaying leaves and nut hulls. Because decaying roots still release juglone, toxicity can persist for a number of years after a tree is removed.