Gerald L. Klingaman
Family
Juglandaceae
Botanical Name
Juglans nigra
Plant Common Name
Black Walnut
General Description
The impressive hardwood tree, black walnut, produces tasty crops of nuts in fall and is considered one of the best North American trees for fine lumber. It is a hardy, deciduous tree that is distributed across the eastern half of North America. In the wild, it is very adaptable and grows in both lowland and upland sites. It develops a broad, rounded canopy when mature, which is supported by a long, broad trunk lined with thick, corky bark that is sandy brown with furrows of darker brown and black.
Black walnut has compound leaves with 10 to 23 leaflets. Each lance-shaped leaflet is drab green with tiny teeth on its edges and a slightly lighter gray-green underside. The leaves emit a spicy odor when crushed and turn golden yellow in fall. As the foliage emerges in mid to late-spring, separate male and female flowers appear along the branches. Dangling chain-like clusters of male flowers are borne on the previous year's growth. Small spikes of greenish yellow female flowers appear on new growth. The male and female flowers do not bloom together on the same tree, the female flowers usually blooming first. Consequently, self-pollination rarely occurs, and multiple trees are required for heavy fruiting. The heavy, globular fruits have a greenish yellow husk that turns brown in fall. The hard, brown nut inside can be broken open to reveal delicious nutmeats.
Black walnuts develop a deep tap root as well as a complex of lateral feeder roots. The roots exude a chemical called juglone, which is toxic to some plants, particularly those in the tomato family (Solanaceae). So, do not plant tomatoes, peppers, eggplant, potatoes or any other member of this family near a black walnut.
This large tree grows best in a spacious location with full sun. It thrives in deep, fertile, sandy or clay loam with average drainage and an acid to alkaline pH. It has few pest and disease problems and is long-lived. Many plants are resistant to juglone and can be planted beneath this tree, including hosta, smooth hydrangea and Canadian ginger.
This is a magnificent specimen tree for spacious landscapes, but it should not be planted near parking lots or areas frequented by people. The dropping nuts can be dangerous and will litter parking lots and sidewalks. The nut husks also stain clothing and surfaces. In fact, they used to be used to make a dark brown dye for textiles. The nuts are excellent for wildlife forage as well as human consumption, and black walnut lumber has a fine grain, dense texture and rich brown color.
