My neighbor has a huge Black Walnut tree in his back yard and I am trying to create a small garden spot in my back yard. I was told that the Walnut tree roots give off a substance that will affect some plants growth. Is this true? What can I do to counteract this substance.
The answer is both yes and no. Let me explain. The roots of black walnut and butternut trees produce a substance known as juglone, which is a growth inhibitor. The toxic zone from juglone can average 50 to 60 feet radius from the trunk of the tree but can be as far as 80 feet. Many plants such as tomato, potato, blackberry, blueberry, azalea, mountain laurel, rhododendron, red pine and apple may be injured or killed within the root zone of these trees because of this substance.
However, not all plants are susceptible. Some understory plants that are not affected include anemone, jack-in-the-pulpit, lady fern, cyclamen, dog’s-tooth-violet, gentian, green hellebore, hosta, iris, lilies, resurrection fern, double-file viburnums and boxwood as well as Japanese Maple, Eastern Redbud, Rose of Sharon, Black Raspberry, Calendula, Pansy, Peach, Cherry, Plum, Hollyhocks, European Wild Ginger, Sweet Woodruff, and Spiderwort.
Vegetables such as squashes, melons, beans, carrots, and corn are immune as well.