The black walnut is a species of deciduous tree native to North America. The botanical name of the tree is Juglans nigra, but it is also called the eastern or American black walnut. The black walnut tree is highly valued for its hardwood, according to the U.S. Department of Agriculture Forestry Service. The nuts are also commercially valuable and are used in baking.
The black walnut species grows primarily in the eastern and central United States, according to the U.S. Department of Agriculture Forestry Service, but they are also seen in the western U.S. The trees most commonly grow from western Vermont, north to Ontario, as far east as parts of Florida and as far south as parts of Texas. They usually grow as individual trees or in small groups tucked into deciduous forests.
Black walnut trees have a neatly rounded canopy that is almost as wide as the tree is tall. In cultivation they usually average about 70 feet in height, according to the University of Florida, but in the wild they can grow to 150 feet. The branches are large and well-spaced and present an attractive profile in the winter. The flowers are green and hang in spikes up to 8 inches long. The leaves are green and ovate. The fruit is round, with a hard outer shell, and between 1 to 3 inches in diameter. They are highly attractive to squirrels.
Black walnut trees enjoy temperate climates, with mild summers and cool winters. They grow best in United States Department of Agriculture (USDA) plant hardiness zones 5 though 9A, according to the University of Florida. These trees cannot tolerate the hot temperatures of subtropical or tropical climates very well.
Black walnut trees grow best in sunny locations but in rich, moist soil. They often grow along riverbanks and streams in the wild. These trees develop long taproots, which means they need very deep, fertile soil. This also makes them difficult to transplant. Black walnut trees planted in the home landscape need a sunny location that has plenty of high-quality, organic soil.
While attractive trees, black walnuts tend to be messy. They drop a lot of twigs, nuts, flowers and leaves. For that reason, they are not great trees to plant in public areas. These trees are also somewhat fragile. They are often affected by insect pests and diseases, according to the University of Florida, including fungal diseases that attack the leaves, insects that eat the leaves, and bacterial diseases that attack the nuts. Sprays can treat insect problems and prevent fungal diseases.
The roots (and all other parts) of the black walnut tree contain a substance called juglone. Some plants will not grow well underneath or near black walnuts because of their sensitivity to juglone. Juglone causes these plants to develop yellow foliage, wilt and eventually die. Such plants include tomatoes and evergreens, according to the University of Florida.