Black Walnut

Native to eastern North America, where it is one of the most valuable hardwood trees.

• Distributed from southern Ontario and New England west to South Dakota and Nebraska, south to Texas, Louisiana, and northern Florida
• Most abundant and reaches its greatest size in the Ohio River Valley and the central Mississippi Valley
• Found at elevations from sea level to approximately 1,000 meters
• A component of rich, moist deciduous forests, particularly on bottomlands and lower slopes
• The name "walnut" comes from the Old English "wealhhnutu" meaning "foreign nut" (introduced to Britain by the Romans)
• Black Walnut timber was so prized that pioneer families would reserve their best walnut trees when clearing land
• Thomas Jefferson planted Black Walnuts at Monticello and called them "the best of all nuts"
• The brown dye from walnut husks was used by early American colonists and Native Americans for textiles and baskets

A large, stately deciduous tree with a broad, rounded crown.

Bark:
• Dark brown to black, deeply furrowed into narrow, interlacing ridges
• One of the darkest-barked trees in eastern North American forests

Leaves:
• Alternate, pinnately compound, 30 to 60 cm long with 15 to 23 leaflets
• Leaflets lanceolate, 7 to 10 cm long, finely serrated
• Dark green above, paler beneath, aromatic when crushed
• Turn bright yellow in autumn

Flowers:
• Monoecious — male and female flowers on the same tree
• Male flowers in dangling green catkins, 5 to 10 cm long
• Female flowers in small terminal spikes of 2 to 3
• Wind-pollinated in late spring

Fruit:
• Large, spherical nuts, 4 to 6 cm in diameter
• Enclosed in a thick, green, fleshy husk that turns black when ripe
• Husk produces a dark brown dye that stains everything it touches
• Nut shell is extremely hard, deeply ridged, and difficult to crack
• Kernel is rich, dark, intensely flavored — considered the finest-flavored walnut

Form:
• 20 to 35 meters tall with trunk diameters commonly 60 to 120 cm
• Crown broad, rounded, with ascending upper branches
• Deep taproot develops early — trees are difficult to transplant once established

The Black Walnut plays unique ecological roles in eastern North American forests.

Habitat:
• Found in rich, moist, well-drained deciduous forests, especially on bottomlands, lower slopes, and coves
• Prefers deep, fertile, neutral to slightly alkaline soils
• Often associated with limestone-derived soils
• Common in mixed hardwood forests with oak, hickory, ash, and tulip tree

Allelopathy:
• Roots, leaves, nut husks, and bark produce juglone (5-hydroxy-1,4-naphthoquinone)
• Juglone is toxic to many plants, including tomatoes, potatoes, peppers, rhododendrons, azaleas, lilacs, and many other garden species
• Creates a "zone of death" around the tree where sensitive plants cannot grow
• Black Walnut and its relatives (butternut, hickory) are immune to their own juglone
• Some plants, including black raspberry, fescue, and zinnias, are juglone-tolerant

Ecological interactions:
• Nuts are a crucial food for squirrels, which are the primary agents of seed dispersal
• Also eaten by wild turkeys, woodpeckers, blue jays, raccoons, and bears
• Host plant for Luna Moth and Regal Moth (Citheronia regalis) caterpillars
• Deep taproot brings nutrients up from subsoil layers

Growth:
• Moderate growth rate of 30 to 60 cm per year
• Long-lived — 150 to 250+ years
• Deep taproot makes it very wind-firm and drought-resistant

All parts of the Black Walnut contain juglone, which is toxic to many plant species and can cause allergic skin reactions in some people. The green husks contain high concentrations of juglone and tannins that can stain skin dark brown and cause contact dermatitis. Walnut sawdust can cause respiratory irritation. Horses are particularly sensitive to black walnut shavings — even bedding containing as little as 20% black walnut shavings can cause laminitis, a painful and potentially fatal hoof condition. Walnuts themselves are non-toxic to humans but can be toxic to dogs and horses if consumed in quantity.

A valuable timber and nut tree requiring careful site selection.

Site selection:
• Full sun
• Deep, fertile, well-drained, neutral to slightly alkaline soils
• Avoid planting near gardens containing tomatoes, potatoes, peppers, roses, rhododendrons, or other juglone-sensitive plants
• Keep at least 15 to 25 meters from garden areas and sensitive ornamentals
• Not suitable for small residential lots due to allelopathy and large size

Planting:
• Plant seedlings or grafted trees in spring
• Difficult to transplant due to deep taproot — use container-grown or small seedlings
• Dig a deep planting hole to accommodate the developing taproot

Care:
• Water during the first 2 to 3 growing seasons
• Very drought-tolerant once the taproot is established
• Minimal pruning needed
• Harvest nuts in autumn when husks begin to soften and turn black
• Remove husks promptly and allow nuts to dry for several weeks before cracking
• Susceptible to walnut twig beetle and thousand cankers disease in western states
• Hardy in USDA zones 4 to 9

The Black Walnut is one of the most economically valuable trees in North America.

Timber:
• Among the most valuable domestic hardwoods — heartwood is rich, dark chocolate-brown with a beautiful grain
• Veneer-grade Black Walnut logs can sell for $5,000 to $10,000+ per tree
• Used for fine furniture, cabinetry, gunstocks, interior paneling, and boat building
• Prized by woodworkers for its workability, stability, and rich color
• Historically used for railroad ties, fence posts, and construction

Edible nuts:
• Kernels are rich, dark, intensely flavored — stronger and more complex than English Walnut
• Highest protein content of any commercial nut (approximately 24%)
• Used in baking (black walnut cake, cookies, ice cream), candy, and savory dishes
• Commercial nut production is limited by the extreme hardness of the shell
• Oil pressed from nuts is used as a gourmet cooking oil

Dye:
• Husks produce a rich brown-black dye used since antiquity
• Used by Native Americans for basketry, textiles, and hair dye
• Used by colonists for ink and fabric dye

Other:
• Shells used as an abrasive in metal polishing and oil well drilling
• Hulls used in traditional medicine as an antifungal and antiparasitic