You may have heard both good and bad reports about black walnut trees. On the one hand, they provide edible fruit for squirrels and other wildlife; on the other hand, they can kill other plants growing in the area. For this reason, you want to know what this damaging tree looks like. In this article, we’ll talk about how to identify the black walnut tree and compare it against a couple of lookalikes.
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What is a Black Walnut Tree?
This tree is beneficial in many ways. Its finely-grained wood is easy to work, resists rot, and is highly valued as lumber; it can function as a desirable shade tree; and it produces sweet, earthy nuts that contain many health benefits and provide food for wildlife in the winter.
So, why is it called a “killer tree”?
Black walnuts produce a secretion called juglone. This secretion functions as a natural herbicide for many plants.
In other words, plants that are sensitive to juglone can’t grow in the vicinity of black walnut trees. Some of these plants include potatoes, tomatoes, eggplant, peppers, azaleas, hydrangeas, blueberries, blackberries, and rhubarb.
All trees in the walnut family, including pecans, butternuts, and English walnuts, produce juglone; but most produce such a small amount that even sensitive plants aren’t affected by it. Black walnuts produce a much greater amount than other trees in their family.
Juglone tends to leach into the soil surrounding the tree through its roots. A black walnut’s root system generally extends outward as far as its canopy, or as much as 75 feet.
All parts of the tree produce juglone, though the highest concentration is found in the roots, hulls, and buds.
If you’re planning to grow juglone-sensitive plants in your yard, you’ll want to first identify any black walnut trees you may have. Grow your plants as far away from these trees as possible.
Where Do Black Walnut Trees Grow?
As mentioned above, black walnut trees are native to the eastern half of North America. In the United States, they can be found just about anywhere east of the Rocky Mountains, from New England to Florida and westward into the Plains states.
Black walnut trees are very hardy and can grow in a variety of soil conditions. They are sometimes found in mixed deciduous forests, where they shed their lower branches and can grow up to 150 feet tall in their competition for light.
They will also grow singly in a number of different environments. They are sometimes planted as landscaping trees, and they often sprout on their own from walnuts previously buried by squirrels.
Black walnut trees growing outside of a forest environment typically don’t grow as tall. Instead, they will “spread out”, developing a wider canopy and retaining their lower branches.
They can be cultivated and grown outside of their native habitat, though extra care may be necessary to keep them alive. They do best when they receive plenty of water and full sunlight.
How to Identify a Black Walnut Tree
Black walnut trees are relatively easy to identify by their fern-like leaves and baseball-sized fruits.
Each leaf is composed of at least 15 oppositely arranged leaflets. These leaflets are about 3 to 5 inches long and a rich yellow-green in color.
The leaves typically appear late in the spring and begin falling early in the autumn. Before they fall, they turn bright yellow.
The fruits are lime green in color and may begin falling as early as late summer. They will continue falling into late autumn, sometimes after the leaves have all been shed.
The fruits begin to turn black shortly after falling. The outer husk can be removed to reveal a hard shell; inside this shell is the edible nut.
Black walnut tree trunks are grayish to brown depending on their age. The bark has a scaly appearance at first, but as the tree matures the bark will develop deep, diamond-shaped ridges.
Black walnut trees are not easily confused with other trees in their own family, which all have unique appearances. That said, they do have a couple of lookalikes:
Tree of heaven
This non-native tree is highly invasive and, during the summer months, can look quite similar to the black walnut. The main reason for this similarity of appearance is the leaf structure: it contains large leaves composed of individual leaflets that give it a fern-like appearance.
That said, there are several ways to tell these two trees apart.
For one, the tree of heaven’s leaves are a little darker and are not serrated as are black walnut leaves. What’s more, the tree of heaven has a very strong, repugnant odor and unique-looking bark similar to the skin of a cantaloupe.
Staghorn sumac is a native tree that shares much of its range with the black walnut. This tree also contains large leaves made up of fern-like leaflets.
That said, staghorn sumac trees are much smaller than black walnuts, and they produce bright red flower clusters in the spring and summer. During the fall, their leaves turn bright red instead of the yellow color walnut trees are known for.
Check out this video to learn more about identifying black walnut trees:
Black walnut trees can be identified by their yellow-green, fern-shaped leaves, ridged bark, and lime-green fruits that turn black after falling in the autumn. It’s important to be able to identify black walnut trees in your yard if you’re planning to have a garden, as the trees produce a secretion that can injure and kill many other plants.