Submitted by ~ Corry Mordeaux
Do Black Walnut trees really poison other plants?
Yes. Many plants are killed when grown within the root spread of the black walnut tree. Butternut and Persian walnut trees grafted onto black walnut rootstocks give the same effect.
Black walnut trees contain a phytotoxin, juglone, which remains in the roots and is not secreted into the soil. For injury to occur the roots of the walnut must contact the roots of other plants growing nearby. Plants closest to the walnut tree are usually injured first but plants up to 80 feet away can be injured because that is the average root spread of a mature black walnut tree. Even after the walnut tree is removed, juglone may remain in the dead roots until they decay.
The wilting caused by a plant’s contact with juglone cannot be reversed or reduced by watering. Stunting, death, or wilting of the whole plant or only a part of it may occur. The side nearest to the walnut tree usually wilts first. Although most plants are affected, even other walnut trees, the problem is most severe on tomatoes, potatoes, and evergreens.
Note: I have a 30 foot Pinus sylvestris (Scots Pine) that is very dead. It was planted about 15 feet from a Black walnut. (Not too smart, Corry.)
Dr. Bob is gone but his wisdom lives on.