Black Walnut, Juglans nigra

I whittled this miniature chain from black walnut wood using only a pocket knife. The wood was beautiful and durable, and easily workable. As I whittled, I thought about the huge black walnut tree in my uncle’s back yard, wishing I had some nuts from the tree.  I also thought about my grandfather’s depression-era story of how he often caught fish by throwing a sack of black walnut husks in the creek to stun them. Black walnut trees have many features and uses, and timber is only one of them.

The black walnut tree, Juglans nigra, is one of the most commercially important trees native to the United States. The tree produces a dark brown hardwood that is highly prized. Walnuts produced by the tree have a distinctive taste that is desirable. Walnut shells are hard and have important commercial uses, primarily as an abrasive. Walnut husks have been used to make dyes, and have important medical uses. Sap from black walnut trees can even be collected for making black walnut syrup. Such syrup is said to have a high pectin content requiring extra steps in production to taste desirable. Black walnuts are native to the eastern United States, and about 65% of the annual wild harvest of black walnuts come from the state of Missouri.

The form of a large black walnut tree that is grown in an open area is very similar to that of an oak tree. The tree has a short trunk and broad crown, which is best for walnut production. The first tree pictured was open grown. However, when the tree grows with forest competition, it develops a tall and straight trunk. This is best for timber production. The tree in the last picture was grown in a forest. Black walnut trees typically grow up to 36 inches in the first year and more in the second year. They have a strong taproot. A black walnut tree can grow to a height of over 100 feet, and live to be over 200 years old. Limbs are strong and widely spaced. Black walnut bark is rough and gray-black. Its deep furrows and thin ridges give the bark a diamond shaped pattern. One important way to identify a black walnut tree is to use a knife to cut in to the inner bark to see if it is chocolate brown in color. Another important identifier is to check for a very characteristic pungent or spicy odor in the cut bark and in stems, leaves, and fruit husks. Yet another identifier is to check to see if twigs have a chambered pith that is light brown.

The fern-like appearance of the black walnut tree’s pinnately compound leaves is interesting. Trees leaf out in late spring when the soil is warm and all danger of frost is past. Leaflets are arranged alternately on stems that measure 1 to 2 feet in length. Each stem holds 15 to 23 leaflets with largest leaflets located in the center, and the terminal leaf is often missing. Leaflets are 4 to 8 inches long, are sharply toothed and pointed, and have a round base. Black walnut leaflets are dark green, and turn bright yellow in early fall. Leaf drop is most often before surrounding trees.

Both male and female flowers are found on black walnut trees. However, self-pollination is unlikely. Female flowers typically appear before male flowers, but sometimes it is the other way around. Varieties should be used together that have beneficial overlap. Male flowers are in drooping catkins 3¼ inches long, and pollen is carried by the wind. These catkins come from axillary buds on the previous year’s growth. Female flowers come from terminal buds, in clusters of 2 to 5 on the current year’s growth. Buds are pale and covered in downy hairs. Flowers appear about mid-April.

The fruit of the black walnut is a nut that ripens in October or November. A round, brownish-green, semi-fleshy husk surrounds a round, brown, hard and wrinkled shell. This shell covers the nut kernel. The husk is typically ¼ to ½ inches thick, and requires much effort to remove. The shell’s many folds make it difficult to remove leaving the nut kernel in one piece, so the kernel is used in pieces. Black walnuts begin to appear when the tree is 4 to 6 years old, and large crops take about 20 years. Black walnut production tends to be irregular from year to year. Black walnut trees thrive in warmer regions with fertile, well-drained lowland soils having high water tables, but they will not grow in wet soil. When grown in drier soils, they are affected by drought. Most of the black walnut trees I have found, including the small one pictured here, were growing along rivers near Helen and Dahlonega, Georgia. I have also seen trees growing in drier, hilly areas near Douglasville, Georgia.

One feature of the black walnut tree that is worth mentioning is the fact that it restricts growth of many competing plants surrounding it by use of a chemical called juglone. This chemical remains in the soil years after a tree is removed, continuing to inhibit growth. This allelopathic feature is common to all walnut trees.

The black walnut tree is one of the most fully utilized trees in the United States. Considering its importance, everyone should know this tree.

Author: David

I grew up near Clayton, AL and have lived over 30 years near Atlanta, GA. My interests include family, church, guitar, gardening, working with kids... and math! Life can be very interesting. My websites: chasingtrees.net mathshortcutblog.wordpress.com View all posts by David