University of Maryland Extension

Walnut Toxicity - Juglone

 March 2019

Walnut Toxicity Update 

It has been an accepted article of faith among horticulturists that juglone, a chemical compound associated with black walnut roots, inhibits the growth of certain plant species growing nearby. Researchers and Extension personnel have developed long, authoritative lists of plants that should and should not be planted near black walnut trees and related species.

Linda Chalker-Scott, Ph.D., Associate Professor and Extension Horticulturist with Washington State University recently wrote a fact sheet Do Black Walnut Trees Have Allelopathic Effects on Other Plants? that digs into this issue. Dr. Chalker-Scott concludes that there is no conclusive, science-based evidence confirming juglone as the cause for the poor growth of plants growing near black walnut trees.

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