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Black Walnut: Massive and Messy

The good, the bad and the nutty

June 2024

Black walnut trunk and canopy

Black walnut trunk and canopy (Photo by Karen Hine via Flickr)

Black walnut leaves and fruits (Photo by Katja Schulz via Flickr)

by Steve Carroll, Contributing Columnist

A landowner with a mature, open-grown black walnut is fortunate indeed, able to appreciate this tree’s massive presence; thick, dark, furrowed bark and flavorful, protein-rich nuts in the fall. On the other hand, a homeowner with a tree whose branches overhang the sidewalk and driveway — not so fortunate, as they must deal with fallen leaves and branches; a barrage of walnuts on the roof, sidewalk and car; and the effects of juglone, a chemical that leaches from walnut parts and interferes with the growth of nearby plants such as vegetables

Black walnut (Juglans nigra) is a striking tree, with brown-black bark, thick twigs and a typically straight trunk. Leaves are 12 to 24 inches long, with 10 to 24 finely toothed leaflets that turn yellow in the fall. These leaves drop earlier than most other hardwoods, and they are slow to leaf out in the spring. Walnuts are classified with hickories (genus Carya) in the walnut family.

Black walnut is an eastern species, native from Massachusetts to the Florida panhandle, and west to South Dakota and east Texas. It prefers rich soil, moist uplands and floodplains, but also grows along fencerows and in old fields — and anywhere a squirrel has buried a nut. It can also be planted well outside its natural range.

Male flowers form in hanging catkins in late spring, with female flowers in small clusters at twig ends. Walnuts are wind pollinated, and if successfully fertilized, fruits mature by the fall. A newly formed walnut seed is enclosed within a hard, ridged shell, which itself is surrounded by a yellow-green husk. Walnut trees typically have both male and female flowers and can, therefore, self-pollinate. However, the resulting fruits may be relatively few or small. Better to plant two or more trees near each other to encourage cross pollination

Walnuts are eaten by many birds and mammals, and the foliage is fed upon by more than 100 moth and butterfly larvae. Some Native Americans ate the nuts fresh, boiled, in soups and as flour, and they used the husks and roots to make dyes. After European settlement, the rot-resistant wood was used for fenceposts, shingles, railroad ties and mill waterwheels, and the fruits were, and still are, used to make dye for yarn and fabric. More recently, the ground shells have been used as an abrasive in the automotive and airline industries.

Today, above all else, black walnut is valued for its beautiful heartwood, which is widely used in making fine furniture, cabinets, church altars, rifle stocks and more. Walnut is also now used to make increasingly thin veneer. Walnut wood is so valuable that landowners have sometimes planted trees as an investment for their grandchildren and great-grandchildren. On the other hand, having trees on your property doesn’t guarantee financial success, as loggers may decline to maneuver large trees and logs around power lines, fences and buildings. Woodworkers may also worry that unseen embedded nails, bullets, pieces of metal fencing or hidden hammock anchors will damage their extremely expensive saws.

Walnut is relatively free of pests, but the spread of a fungal infection called thousand cankers disease in the western U.S. is causing concern.

Do you have black walnuts on your property? Perhaps you should do as in earlier times and host a fall “nutting party.” Invite your friends and neighbors over to help shell the fruits, appreciate the rich, oily taste of the nuts, and prepare a few pounds of nuts for your winter cooking and baking. 

Steve Carroll is a botanist and ecologist who speaks and writes about trees, gardening and the world of plants. He is the co-author of “Ecology for Gardeners,” published by Timber Press.