Black Walnut Is a Common North American Tree

Black Walnut Is a Common North American Tree

Black walnut used to be a very common old-growth forest tree. Black walnut wood is now relatively scarce and highly coveted, used mainly for high-quality woodworking. The tree hates shade (intolerant) and best growth occurs in a sunny open location and a moist rich soil, common along stream banks in its native habitat.

The Black walnut produces a substance that is toxic or "allelopathic" to other plants called juglone. Tomatoes and coniferous trees are especially sensitive. This mild toxin helps the tree keep other vegetation from competing for valuable nutrients and moisture.

Black walnut grows with a rounded crown to about 70 feet (can reach 100 to 150 feet in the woods) and spreads 60 to 80 feet when open grown. The tree grows rapidly when young but slows down with age and develops with a number of massive branches well-spaced along the trunk forming a very strong, durable tree. While valued as a lumber tree it may not make the best yard tree. The nuts are edible but are a nuisance to clean up and leaves often fall prematurely from some types of leaf disease.

Description and Identification of Black Walnut

USDA-NRCS PLANTS Database/Wikimedia Commons

Common Names: American walnut, eastern black walnut

Habitat: Black walnut typically grows as scattered individual trees or in small groups throughout the central and eastern parts of the United States. Although it is found on a variety of sites, black walnut grows best on good sites in coves and well-drained bottoms in the Appalachians and the Midwest.

Description: Under forest competition black walnut develops a tall, clear trunk. The bark is grey-black and deeply furrowed. The "chambered" pith of the twigs contains air spaces and is a key identification feature. The leaves are alternate, odd-pinnate with 15 to 23 leaflets with the largest leaflets located in the center. The male flowers are in drooping catkins and the fruit ripens in fall into a brown corrugated nut with a brownish-green, semi-fleshy husk. The whole fruit, including the husk, falls in October; the seed is relatively small and very hard.

Uses: The fine straight-grained wood makes prize pieces of solid furniture and gunstocks. High-quality black walnut is also used as veneer attached to woods of lesser value. The distinctive tasting nuts are in demand for baked goods and ice cream.​

Natural Range

Elbert Little/U.S. Department of Agriculture, Forest Service/Wikimedia Commons

Black walnut's natural range extends from western Vermont and Massachusetts west through New York to southern Ontario, central Michigan, southern Minnesota, eastern South Dakota and northeastern Nebraska; south to western Oklahoma and central Texas; excluding the Mississippi River Valley and Delta, it ranges east to northwestern Florida and Georgia. On the western fringe of its range in Kansas, walnut is fairly abundant and frequently makes up 50 percent or more of the basal area in stands of several hectares.​​

Silviculture and Management

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"Trees produce a strong tap root on well-drained loose soils and recover poorly after transplanting. Trees with trunks to five feet in diameter can be found in the eastern part of the country. A yellow dye is made from the fruit husks. The seed is used in candy-making, cleaning abrasives and explosives.

The tree is probably best used in a park, campus or other open space area. However, the fruit is very hard and can dull a lawn mower blade quickly and a mower can 'shoot' the fruit across a lawn at a high rate of speed, possibly injuring people in the area.

Place the tree so it will receive an adequate supply of water. It is not drought tolerant, often dropping leaves in dry spells and is poorly adapted for urban soils. It is really most happy in the loose gravely soil of stream banks and other undisturbed areas but tolerates alkaline and wet soil."

- From Fact Sheet on Black Walnut - USDA Forest Service

Insects and Diseases

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Pests: Fall webworm larvae web over branches then feed on leaves inside the nest. Nests can be pruned out of small trees or use sprays of Bacillus thuringiensis.

Tent caterpillars also eat foliage in the spring. Scales of various types attack walnuts. Most scales can usually be controlled with horticultural oil applied. The leaves may be eaten by any one of several caterpillars. These can be controlled with sprays once identified.

Mites cause speckling and yellowing of the leaves.
Diseases: Brown leaf spot or anthracnose symptoms are irregular dark brown spots occurring in early summer. Severely infected trees may be defoliated. Rake up and destroy infected, fallen leaves.

Canker diseases cause dieback or death of trees. Infected bark may be discolored, sunken, or have a different appearance than surrounding healthy bark. Bacterial blight causes small, irregularly-shaped spots on the leaves and leaf stems.

Black spots occur on young nuts and shoots. Nearly ripe nuts have large black spots on the husks. Infected nuts fall prematurely or may have husks, shells, and kernels blackened and ruined.

Powdery mildew causes a white coating on the leaves. During periods of high temperature and drying winds, walnuts may scorch. Make sure plants have adequate soil moisture.