Walnut trees grow in the forests of the eastern United States. Trees grown in the open sun typically reach 70 feet high and spread 60 to 80 feet wide. The walnut's fruit is a round, shelled nut, 1 to 3 three inches in diameter. The outer shell is typically green but turns black after falling to the ground. Squirrels often consume the edible kernel. Several industries use walnut husks in industrial formulations, such as insecticides, filtering agents and propellants.
Walnuts produce an allelopathic substance known as juglone which inhibits the growth of other plants. Trees exude the chemical into the soil through the roots. Juglone is also present in the leaves, branches and bark. The chemical can inhibit, damage or kill nearby plants. Some plants, such as hydrangea, Norway spruce and mountain laurel, cannot grow within 50 feet of a walnut tree's drip line.
Thousand canker's disease is a current threat to the species. This fungal infection spreads via the walnut twig beetle. The disease has spread from the western United States into the walnut's native range in Tennessee, Virginia and Pennsylvania.
People use walnut lumber for making furniture and gun stocks. As of 2015, it most commonly finds use as veneer due to shrinking populations from heavy logging in native forests.