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Resources < Wildlife Habitats < Guide to Native Plants of Georgia for Wildlife < Juglans nigra
Black Walnut is a remarkable native nut tree with a long history of use as a food, a dye, for wood, and as a medicinal plant. Like other members of the Walnut family, Black Walnut is allelopathic. All Walnuts produce a biotoxin called juglone, which inhibits the growth of nearby plants. Other plants must make direct physical contact with Walnut parts in order to be affected. Juglone is concentrated most highly in root tissues and fruit husks, with lesser amounts in the leaves, catkins, buds, and inner bark. Leave a wide spacing between Butternuts and other plants and trees which it may kill. The most sensitive plants to juglone are nonnative plants, because unlike native plants, they have never developed an evolutionary resistance to the chemical. The chemical is nontoxic to people and animals.
Black Walnuts are excellent for making baked goods, candies, and yield an excellent oil and flavor. They become rancid soon after maturing, so pick and use them quickly. Nut production begins at around age 20.
Aside from the nuts, Black Walnut has great value in a variety of other ways. . It is one of the most valuable North American hardwoods in fine woodworking and shines extraordinarily well with polish. It is used in the manufacture of furniture, woodcarvings, and a variety of other projects. Black Walnut bark and nut rinds were formerly an important dark brown dye. Colonists, settlers, and Confederate soldiers made home-made clothing dyed with it. Black Walnut’s outer bark was formerly used in medicinal teas for treating toothaches and dysentery. The inner bark has been used as a cathartic, and during the American Revolution was employed in treating smallpox, dysentery, and other gastronomic disorders.
Black Walnut differs from Butternut in the flavor of its nuts. Both types far exceed the flavor of cultivated, nonnative walnuts found in grocery stores. It grows larger, spreads much wider, and is altogether a better ornamental tree than Butternut. Its massive size and spread at maturity rivals the Live Oak in beauty.
Juglandaceae (Walnut)
A large, vigorous, deciduous, nut-producing hardwood tree with a long, clear bole and open, spreading crown. Bark is dark brown, especially under the surface, ridged and furrowed, and has a rough diamond pattern. Leaves are alternate, pinnately compound, 12-24” long, and possess 10-24 leaflets. Leaflets may be poorly formed, often with terminal leaflet absent. They are ovate-lanceolate, finely serrated, 3-3 ½” long, with a stout and pubescent rachis. Flowers are monoecious and appear in late spring. Males are single-stemmed catkins, 2 ½-5 ½” long; females appear on short spikes near twig ends, and are yellow-green in color. Fruits are round, 2-2 ½” in diameter, with thick, green, indehiscent husks. Husks are irregularly furrowed. Nuts are hard, with sweet, oily meats, and mature in late summer to fall.
70-100 feet tall, 150 feet tall in optimal conditions, and a massive 70 foot crown spread in open areas
A large, vigorous, spreading, deciduous, hardwood, nut-producing tree
Slow
Full sun required for best fruiting; intolerant of shade
Black Walnut requires good drainage and is intolerant of shade. Like other walnut species, it produces a biotoxin called juglone that inhibits the growth of many other plants without resistance to the toxin. Plant with wide spacing between Black Walnut specimens, and keep away from other beloved plants. Sow nuts in the final desired location, as Black Walnut’s taprooted growth causes transplants to rarely succeed.
Black Walnut has high ornamental value in its exquisite and unusual bark. It is not only interestingly patterned, but very dark in color. The foliage, fall color, and nuts are also visual assets.
Because of Black Walnut’s allelopathic (toxic) tendencies, plant with a great deal of extra spacing between specimens. Also, do not plant where its toxins may compromise the growth of or kill other beloved trees or plants, especially nonnatives. Plant trees in rows or groups to ensure adequate pollination. The litter of the plant will cause staining on surfaces that it contacts, especially wood and concrete. Do not plant where litter will become a problem.
Nuts are eaten by a variety of small mammals including squirrels, chipmunks, and other rodents. The leaves and young twigs are browsed by deer. Black Walnut leaves, along with Butternut, together host over 100 species of Lepidoptera (butterflies and moths), which in turn feed birds and ultimately predatory birds, reptiles, and mammals. Specialist species that eat no other trees include the Walnut Caterpillar, Angus’s Datana, and the Gray-Edged Bomolocha. They are also preferred hosts for the beautiful Luna and Regal moths.
Native to North America from Massachusetts and Ontario southwest to Nebraska, south to Texas, and east to Georgia. It prefers deep, moist, fertile soils found in areas of alluvial deposition like river floodplains.
Nuts stratified for 2-4 months; sow in fall for best results; transplants rarely succeed
Text by Kevin Tarner, Georgia Wildlife Federation
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