By Mort Schmidt for Simply Living
Black Walnut (Juglans nigra)
Black Walnut (Juglans nigra) is one of our most prized hardwoods. Its rich color, hardness, stability, and workability make it the traditional choice for furniture, gunstocks, veneer, and other objects. Of course, walnuts are also edible, but the English walnut (J. regia) is much more widely eaten today, owing to its thinner shell and milder taste. The ancient Romans called walnuts “Jupiter’s Acorn”, in Latin, “Jovis Glans”, which evolved into Juglans.
Black Walnut has alternately-arranged, pinnately-compound leaves. Alternately-arranged leaves are attached to the tree at different points, whereas oppositely-arranged leaves are attached directly across from one another. Black Walnut leaves are pinnately-compound. That is, the leaflets are attached to the stem at various points, while palmately-compound leaves have leaflets attached to the stem at a single point.
Notice that on pinnately-compound leaves, the leaflets are sometimes arranged on their shared stem in alternate or opposite fashion on the same tree, without regard for the overall arrangement of alternate or opposite leaves and branches.
The compound leaves are up to 24 inches long, with 10 to 22 leaflets, lance-shaped, and 2.5 to 5 inches long, with small teeth. Notice that the number of leaflets was described in even numbers, rather than odd. That’s because typically there is not one terminal leaflet at the end of the stem – there are two. The closely-related Butternut (Juglans cinera) and the more-distantly related hickories have an odd number of leaflets, i.e., they have a single terminal leaflet. Black Walnut leaves turn yellow to brown in autumn.
Black Walnuts lose their leaves earlier than most other trees, and they leave in their place a distinctive leaf scar, often compared to monkeys’ faces. The gray terminal buds are also a distinctive sign of Black Walnut in winter.
J. nigra flowers consist of green catkins in early spring. Plants have a number of strategies to prevent self-pollination. Some, like Sassafras and Staghorn Sumac are dioecious, having female flowers on some trees and male flowers on others. Some, like Norway Spruce, have female cones high on the tree and pollen-producing parts lower down, so that their pollen will usually be carried by the wind to other trees. Black Walnuts are monoecious, having female and male flowers on the same tree, but they’re dichogamous – they produce female flowers before male flowers. However, the male and female flowers overlap just enough that some self-pollination can occur in the absence of other Walnut trees.
Black Walnut fruits are approximately 1.5 to 2.5-inch spheres with rough green hulls covering thick, deeply-furrowed shells. The nutmeats, like pecans or the familiar English Walnut, occur as two brain-shaped meats. Because walnuts consist of a single woody seed with a fleshy cover, they are not true nuts, they’re drupes, like cherries, apricots, and plums. Acorns, with their hard exteriors, are true nuts. Like other walnuts, hickories, and oaks, Black Walnuts yield most or all of their nuts during mast years. The populations of rodents and other foragers are limited to the availability of food during lean years. Then, during mast years, more fruits are produced than the foragers can eat, and the trees have a better chance of producing offspring.
J. nigra has dark, rugged bark with a somewhat diamond pattern in its early years, and a blocky pattern in maturity. The twigs are even more distinctive. Like its relative, Butternut, Black Walnut twigs have chambered pith when cut lengthwise. Slicing through a small, fresh twig reveals numerous thin walls that might help regulate the flow of sap. Black Walnut saplings resemble Tree of Heaven (Ailanthus), but Ailanthus lacks chambered pith.
Mature Black Walnuts typically have a height of 70 to 90 feet and a trunk diameter of two to four feet. Ohio’s Champion Black Walnut, located in Delaware County, has a height of 103 feet, a trunk diameter of 5.6 feet, and a crown width of 103 feet.
Black Walnut trees exude juglones, a class of chemicals that kills surrounding vegetation. The ability to kill other plants with chemicals is known as “allelopathy” and it reduces the competition for water and nutrients. Tomato plants are famously sensitive to juglones, but some plants, including Pawpaws, are not, and can be planted near Walnut trees. Juglones also discourage the growth of insects, fungi, and even Walnut’s own offspring.
Butternut (not to be confused with Bitternut Hickory) is Black Walnut’s nearest relative in Ohio, and the most likely to be confused with Walnut. Butternut’s single terminal leaflet, the smaller, lemon-shaped nut, and the more T-shaped leaf scar will help distinguish it. Butternut is far less common than Walnut, and distinguishing between them is seldom necessary. Tree of Heaven leaves are similar to Black Walnut’s, but much larger, its leaflets have only a few teeth near their base. and the leaf scars are far larger and horseshoe-shaped.
ID Summary: Black Walnut has pinnately-compound leaves, typically with two terminal leaflets. The dark brown bark has a coarse diamond to blocky texture. Winter traits include twigs with gray terminal buds, chambered pith, and monkey-face leaf scars.
Juglans nigra occurs in most of the eastern United States, except for New England. Walnut prefers moist, well-drained soils, preferably with open sun. Black Walnut can cross-pollinate with other walnuts, but not Butternut. Walnut trees can survive for up to 200 years.
Black Walnut lumber has a Janka hardness of 1,010 lbf and a density of 0.61 g/cc, according to the Wood Database, compared to the median of my list of 73 Ohio trees of 1,075 lbf and 0.64 g/cc. Black Walnut is unusually rot-resistant, but is seldom used for exterior furnishings due to its cost. Walnut has good working properties, and takes finishes well. Walnut lumber is valued for furniture, veneers, turned objects, and traditionally, gunstocks. Walnut burls, which are knobby protrusions from tree trunks that form as a response to damage, are especially valued for veneers.
The uses for Black Walnut by Natives are too numerous to list, but here are some, according to the Native American Ethnobotany Database:
- Food, in dry form, but also made into soups and mush,
- Wood for furniture and carved objects,
- Dermatological aids, in the form of decoctions from roots, bark, nut hulls, and leaves, applied directly to the skin,
- Anthelmintic (worm removal) made from infusions of bark, roots, and nut hulls,
- Black dye extracted from bark, roots, and nut hulls, and
- Leaves scattered on floors to discourage fleas.
According to Rebecca Rupp’s Red Oaks and Black Birches, Walnut shells carved into the shape of birds and made into ear rings were found in the Indian mounds of Ohio and Indiana. Rupp also reports that the Indian impersonators in the Boston Tea Party dyed their hands and faces with a stain made from Black Walnut husks.
Historically, the combination of rot-resistance, strength, and stability made Walnut lumber useful for the construction of water wheels. Walnut’s structural stability, rot resistance, and hardness made it appropriate not just for gunstocks, but for early airplane propellers, making it an essential resource in earlier wars. In fact, prior to World War I, Germany’s Kaiser Wilhelm II stockpiled American Black Walnut as war materiel. During the Civil War, soldiers used Black Walnut bark to staunch bleeding. They also believed that carrying a Walnut would prevent rheumatism.
According to William Carey Grimm’s The Illustrated Book of Trees, trappers used to boil their steel traps with the husks of walnut shells. This imparted a gunmetal blue surface to the traps which prevented rust.
An Italian liqueur known as “nocino” (or in France, “liqueur de noix”) is made from green walnuts. The recipe calls for soft, green walnuts, vodka or other distilled liquor, sugar, and spices, including cinnamon, clove, or vanilla.
According to the ancient Doctrine of Signatures, the similarity of walnut fruit to the brain indicated that walnuts were effective at treating various problems with the head, such as headaches and mental illness. Inexplicably, walnuts were also supposed to protect one from lightning, witchcraft, and epileptic fits.
Walnut fruits are an important food source for rodents. The leaves are consumed by larvae of the Luna Moth (Actias luna), Regal Moth Citheronia regalis), and Banded Hairstreak (Satyrium calanus).
Walnut wood’s beauty and utility, together with the tree’s attractive form, ensure that it will long be held in high regard.
