Black Walnut Toxicity

Black walnut toxicity affects plants.

Black walnut toxicity refers to the inhospitable environment underneath or near your black walnut tree. Many types of plants can wilt and die if planted too close to a black walnut tree, while other common plants can survive.

Cause

Black walnut trees produce a chemical called juglone, which is common in the roots, nut hull and buds. The chemical deprives plants of energy and causes toxicity. English walnut trees don't produce much juglone; however, sometimes English walnut trees are grafted onto black walnut rootstock, thus causing toxicity.

Symptoms

Plants suffering from black walnut toxicity will develop yellow leaves and will wilt and eventually die.

Range

As your black walnut tree grows, so does the range of walnut toxicity. Ohio State University horticulturists estimate that the average mature tree has a 50- to 60-foot toxicity range, with a maximum toxicity range of 80 feet.

Fun Fact

Other nut trees also produce juglone, but in small enough amounts that no adverse effect is noted on plants. These trees include pecan, hickory, English walnut and butternut.

Prevention/Solution

Plant only tolerant plants near your black walnut tree and avoid locating gardens near the site. Tolerant plants include clematis, rose of Sharon, pansy, zinnia, carrots, melon, hollyhock, snowdrop and hosta.

Warning

Plants that will not survive if planted near black walnut trees include columbine, Asian lilies, silver maple, Norway spruce, blackberry, mountain laurel, rhododendron, peppers and tomatoes.

References

• West Virginia University: Black Walnut Toxicity
• Ohio State University: Black Walnut Toxicity