The prized Black Walnut – In Profile – trees

The prized Black Walnut – In Profile – trees – Brief Article

Jeff Ball

For Americans, there’s no uncertainty about the eastern black walnut (Juglans nigra): Either you love it or you hate it. On the plus side, the tree offers some of the finest wood available to craftsman; on the negative side, it can make life miserable for vegetable gardeners.

Native to the Northeast and upper Midwest, the black walnut has been a useful and desirable tree for more than 300 years. Native Americans and pioneers made a brown dye from the thick husks that surround the nuts. Early pioneers in search of homesteading land looked for black walnut trees, knowing they require rich, well-drained loam that is slightly alkaline. Land that grew black walnuts would be fertile and therefore a good place to settle.

During colonial times it was the tree to have when building fine furniture, until the latter half of the 18th century, when black walnut was replaced by mahogany as the fashionable choice. As was common for the times, a house owned by Abe Lincoln was built with braced-frame oak construction but the exterior and interior trim, doors, siding, and shingles were black walnut.

Proving itself useful in World War I, the tree supplied husks, which were made into high-quality charcoal for gas mask filters, and wood for airplane propellers. In the 1930s the husks found a new use: ground into a type of “meal,” which was then used as an insecticide.

The tree’s durable wood has been used to make everything from sailing vessels to cricket bats. Over the centuries our love affair with its beautiful grain and lustrous appearance has inadvertently created a problem for the tree as a plant. For centuries we harvested only the biggest and best, leaving the weaker trees behind, which eventually seriously weakened the gene pool.

In the past 40 years, tree research facilities, such as one at Purdue University, have been addressing the problem and spending serious time and money to bring back the genetic strengths it offers and which helped make the trees so popular.


As a native species, black walnut grows comfortably as far north as the Great Lakes and Ontario, up to northern New York and along the Atlantic seaboard into New England as far as Maine (UDSA Growing Zone 4) and west to South Dakota. Heading south, the tree grows well to central Texas, Georgia, and along the Atlantic coast into South Carolina (Zone 8).

In the American woods, black walnut trees often appear along forest edges where they get the light and space they need to thrive. They prefer moist, well-drained loamy soil that is neutral or a bit on the alkaline side (pH 6.6 to 8.0). Like most trees, they prefer full sun but will tolerate light shade. Walnut trees can also grow in small groups or as scattered specimens mixed with American elm, hackberry, boxelder, sugar maple, green and white ash, basswood, red oak, and hickory.

They are big trees, soaring 75 to 100 feet tall at maturity with a canopy that typically spreads as wide as the tree is tall. Because their new twigs emerge each spring from buds several inches back from and on the underside of the previous year’s twig tip, the trees develop a distinctive but not always attractive shape. Straight and branchless to nearly two-thirds the distance from the ground, the black walnut’s trunk can, at maturity, measure from 2 to 4 feet in diameter. The branches make abrupt, zigzag turns, sometimes running almost horizontal to the trunk. Eastern black walnuts mature in about 150 years and can live for 250 years.

The leaves are yellowish-green when they unfurl in late spring and remain so until they turn a dull yellow in the fall. They have fuzzy undersides and a noticeable odor when bruised. Male and female flowers grow on the same tree. Though the female flowers are inconspicuous, the male’s appear as 4-inch long, drooping yellow-green spikes in late spring just as the leaves emerge.

By late summer hard-shelled nuts about 2 inches in diameter form inside protective husks. Initially green, the husks turn black as they mature, then break open to release the hard, ridged nut within. The very desirable nut meat is sweet, oily, and high in protein.


There are two very good reasons why this is such an important tree in the American forest: cabinets and ice cream. Black walnut is valued for both the absolutely wonderful cabinet wood it produces and the high-quality edible nuts it bears. As far as I’m concerned, black walnut ice cream is reason enough to plant this tree.

The tree doesn’t have great commercial value in terms of nut production. Something over 23,000 metric tons of black walnuts are harvested annually in the United States, compared to hundreds of thousands of tons produced by English or Persian walnut trees, grown primarily in California.

Black walnut production is based entirely on hand-harvested nuts from trees that are growing in native stands throughout the Midwest and Northeast. The shells of the black walnut are harder than those of the Persian walnut, which makes it more difficult to recover enough nutmeat to make the process sufficiently profitable.

The rich nut meats that do get harvested are used in making my favorite ice cream, in commercial baking, candy production, and in direct retail sales. In reality, there would be no black walnut industry if nuts were the primary crop.

The industry functions as much because there is a market for ground-up black walnut shells. That ground meal goes into products that are used for metal cleaning and polishing, in oil well drilling, and as an ingredient in paint and explosives. In addition to cabinets and furniture, black walnut has been used for musical instruments, paneling, gunstocks, and other fancy wood products. The wood is dark purplish-brown, with a fine grain and luster.

Top-quality logs are sliced into veneer, which then is glued to wall panels, doors, furniture, and cabinets. Logs with significant defects such as large limbs, knots, decay, or crook often can be sawn into gunstock blanks. Even portions of trees that are unsuitable for lumber may be cut for novelty items. Figured wood from the stump, large branch crotches, and burls are especially desirable.

It remains one of our most valuable tree species, based on price per board foot. The black walnut’s beautiful color, strength, durability, stability after drying, and excellent machining qualities keep it in high demand.

But don’t start spending the money you think you’ll get from your own backyard tree quite yet. While reports exist of people getting more than $20,000 from a single black walnut, that kind of money goes only to the very special, very large trees that are getting more and more scarce. But take heart. With new cultivars coming out of research facilities throughout the country, we can expect the black walnut to provide us with wonderful wood and nuts for ice cream for many centuries to come.


Consider your landscape carefully before planting a black walnut, Some consider the shape unattractive and the nuts can cause a mess if they get underfoot–or under car tires. The trees don’t do well with poor urban or suburban soil. They’re at their best in naturalized or wooded areas where they can have lots of light and space.

They also make good individual specimen trees in a spacious yard. Some gorgeous black walnuts can be found throughout many parts of the United States in public areas such as parks and golf courses, as well as in larger residential yards where they can be seen serving as shade trees of imposing dimensions.

If you are planting a tree to produce nuts, begin to look for them after 10 to 12 years. But don’t expect a high-production crop of a bushel or more until the tree is at least 30 years old. Expect a good nut crop in about two of every five years and plan for major competition from your local squirrel population.

Although their nuts are highly sought after, black walnuts can prove toxic to other plants and certain animals and can be an allergen to humans as society expands.

The chemical juglone, found in black walnut’s roots, leaves, trunk, and nut husks, can seriously inhibit the growth of many common garden and landscape plants. Because this stuff is in the roots of the tree, the effect reaches out well beyond the drip line of the tree. Juglone is the black walnut’s evolutionary means of protecting its territory and assuring the good sunlight necessary for its growth. Keep in mind, that its reach can extend beyond the drip line of the tree.

Not all plants are sensitive to juglone, however, and many trees, vines, shrubs, groundcovers, annuals, and perennials happily grow in close proximity to walnuts. Some of the plants that could be killed or harmed include: tomatoes, potatoes, domestic grape, lilac, hydrangea, chrysanthemum, paper birch, red pine, Scotch pine, apple trees, rhododendron, azalea, laurel, blueberries, hemlocks, arborvitae, sweet gum, American holly, and black ash. The toxic effect can remain for quite a few years after a tree has been removed.


Down on the farm, black walnuts are a boon for cows but potentially not so good for horses and dogs. When horses are bedded on wood shavings containing more than about 20 percent black walnut shavings, clinical signs of laminitis, an inflammation in hoof, can occur within 12 to 18 hours. Juglone is not to blame here, although scientists are still unsure which toxin is at fault.

Horses in a pasture that contains black walnuts may show mild respiratory signs from the pollen or fallen leaves. Dogs, too, can get sick from eating the seed hulls, although the larger question is why they’d want to.

The trees are a boon for cows, which enjoy standing in their shade because bothersome flies and other insects tend not to follow them under the trees.


Species: Black walnut (Juglans nigra)

Location: Sauvie Island, Oregon Circumference at 4.5 feet: 278 in.

Height: 130 feet

Crown spread: 140 feet

Total points: 443

Nominator: Dan Tillman

The National Register of Big Trees is sponsored by The Davey Tree Expert Company.

Jeff Ball writes from his home in Attica, Michigan.

COPYRIGHT 2002 American Forests

COPYRIGHT 2002 Gale Group