Black Walnut Trees: Facts, Juglone Effects, and How to Harvest Walnuts

The black walnut tree (Juglans nigra) is one of North America’s most valuable and beautiful native trees, but it does have a “dark side.” Here’s what you should know before planting a black walnut in your yard—and how to harvest and eat the tasty black walnuts too!

Facts About the Black Walnut Tree

• The easily worked, close-grained wood of the black walnut has long been prized by cabinet- and furniture-makers for its attractive color and exceptional durability. Black walnut logs are in such demand for veneer that “walnut rustlers” have made off with trees in the dead of night and even used helicopters in their operations.
• Early settlers discovered black walnuts growing in mixed forests from Canada to northern Florida and west to the Great Plains. They found that their rich-brown heartwood was exceptionally resistant to decay and used it for fence posts, poles, shingles, and sills.
• When surrounded by other trees in the forest, black walnuts grow straight and tall with few, if any, lower branches.
• When planted in the open, the tree will branch out closer to the ground, developing a spreading shape that makes it easier to harvest its sweet, round, 2- to 3-inch nuts.
• Settlers snacked on the nutritious walnuts out of hand, added them to soups and stews, and ground them into a meal for baking; the hard shells provided a perfect package for storing the nuts over winter.

What Is Juglone?

Although the black walnut has many uses and benefits, the tree does come with a caveat: the black walnut’s roots, which may extend 50 feet or more from the trunk, exude a natural herbicide known as juglone. This substance is also found in the tree’s leaves and fruit husks.

Juglone does serve a purpose, though. It inhibits many plants’ growth under and around the tree, thereby limiting the tree’s competition and leaving more water and nutrients for itself. 

Tomatoes, potatoes, apples, pears, berries, and some landscape plants such as rhododendrons, azaleas, and lilacs may be killed or stunted if grown close to black walnut roots or within the tree’s drip line (i.e., under the tree’s canopy). Plan your landscaping accordingly!

A Great Shade Tree

Black walnuts make great shade trees for larger properties. They commonly grow to 50 feet or taller and about as wide, but specimens of more than 100 feet have been recorded.

Black walnut’s large, fernlike foliage provides light, airy shade for those grasses and ground covers unaffected by juglone. The leaves turn bright yellow in autumn, contrasting nicely with the tree’s rugged, dark bark.

Black walnuts require deep, fertile soil with a near-neutral or slightly acidic pH. They are pretty much disease-free and are threatened by a few pests.

How to Harvest Black Walnuts

Thud! Thud! Most walnut tree owners have a love/hate relationship because of the fruit the tree drops in late summer through October. The fruit is quite heavy, the size of a baseball, and lime green in color. It makes quite a mess and can be viewed as a nuisance.

Walnut tree owners will spend hours picking up the fruit in some years. If you don’t remove the nuts, you’ll trip over them in the dark for the rest of the year (while they rot and mold on your lawn). Hire the kid down the street to pick up those dropped walnuts (just be careful not to pay per nut—you’ll go broke)! 

If you’re willing to crack the outer shell, the “meat” inside is edible, as the squirrels will attest; squirrels have little problem chewing through the shells. (Note: Black walnuts are different from English walnuts, which are more commonly sold in stores and shown in the photo above.) 

The sweet, earthy nutmeat inside is well worth the effort. Your grandparents may have harvested walnuts, which can be eaten raw or added to baking (cookies and bars). They can also be used as toppings on ice cream and cakes, enjoyed as a sweetened candy nut, or ground into a meal for a unique flour. 

How to Harvest Black Walnuts

• To harvest, collect the nuts as soon as possible to avoid mold and remove the husks immediately.
• Wear gloves as the husks stain your hands (and anything they touch). If the nut is too hard, wait a few days, and it will brown and soften up.)
• To remove the husk, you can step on them gently with an old pair of shoes. Hose down the nuts in a large bucket to remove any remaining husk.
• Dry the walnuts for a couple of weeks on a screen, drying rack, or in a hanging mesh bag. You can store them unshelled for up to a year.
• Crack the shell with a hammer to get to the nut meat. (Strike at a 90-degree angle to the seam until the nut cracks). Use pliers to easily clip away the shell to release the nutmeat.
• Allow the freshly removed nutmeat to dry for a day before storing.

Do you have a black walnut tree? Please share your comments, questions, and advice!