The black walnut (Juglans nigra) is a large deciduous tree native to eastern North America, valued for its edible nuts and highly prized timber. The tree is the most valuable North American hardwood species by timber value, with figured walnut veneer commanding among the highest prices per board foot of any wood. Black walnuts produce a rich, distinctive-flavored nut that is harvested for baking and culinary use. The tree is also notable for its allelopathic properties, which prevent many other plants from growing beneath its canopy.
Black walnut has been used by indigenous peoples of North America for thousands of years. The nuts were a significant food source, and the husks were used for dye and medicine. European colonists recognized the value of the wood for furniture and gunstocks, and the tree was heavily harvested through the 19th and 20th centuries.
The timber value of black walnut led to widespread planting and management. Black walnut plantations were established throughout the Midwest, and the tree was planted as a shade tree on homesteads. The nut crop gained commercial importance in the 20th century, with Stoke's Black Walnut cracker becoming a standard homestead tool for processing the hard-shelled nuts. The tree is now considered a high-value agroforestry crop.
Black walnut trees grow 70 to 100 feet (21 to 30 meters) tall with a spread of 50 to 75 feet (15 to 23 meters). The bark is dark brown and deeply furrowed. The leaves are compound, 12 to 24 inches (30 to 60 centimeters) long. The nut is enclosed in a thick green husk that stains everything it contacts a dark brown. The shell of the nut is extremely hard and requires a heavy nutcracker or hammer to crack.
The most significant characteristic of black walnut is its allelopathic compound, juglone. This chemical is found in all parts of the tree, particularly the roots and husks, and is toxic to many garden plants, including tomatoes, peppers, potatoes, and azaleas. Sensitive plants within the root zone (extending well beyond the canopy) will wilt and die. Juglone-tolerant species include most grasses, beans, squash, and corn.
Black walnut trees are grown for timber and nut production on homesteads with sufficient space. The wood is used for furniture, cabinetry, flooring, and gunstocks. The nuts are harvested for baking, confections, and nut oils. A mature tree can produce 50 to 150 pounds (23 to 68 kilograms) of nuts in a good year.
The 40 to 60 year rotation for timber means black walnut is a long-term investment. The tree is not suitable for small properties due to its large size and allelopathic root zone. Nut processing is labor-intensive due to the hard shell, but the kernels are highly valued in the specialty food market.