How long does juglone last in the landscape after the removal of a walnut?

Question: 

How long does juglone last in the landscape after the removal of a black walnut?

Answer: 

Juglone is a chemical that inhibits the growth of certain plant species.  When plants produce a chemical that prevents the growth of other plants, it is called allelopathy.  Black Walnut is a common woodland and landscape tree in the Midwest that produces juglone which causes an allelopathic response (inhibition of growth) in other plants.

Juglone is produced by all parts of Black Walnut (leaves, stems, fruit, etc.), making it a highly effective competitor for space in the landscape.  The name juglone comes from the scientific name for Black Walnut, Juglans nigra.  Other members of the Juglandaceae family (includes Butternut and Pecan) also produce juglone, but Black Walnut produces the most and it does it more effectively than other members of the family.

Juglone breaks down quickly in the environment.  Even though all parts of a walnut produces juglone, a few months after removal most of the juglone is gone.  It is usually safe to replant the next growing season in spaces formerly occupied by walnuts.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on . The information contained within may not be the most current and accurate depending on when it is accessed.