Can I use woodchips from black walnut as mulch in my landscape?
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. When plants produce a chemical that prevents the growth of other plants, it is called allelopathy.
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 (includeing Butternut and Pecan) also produce juglone, but Black Walnut produces the most and it does it more effectively than other members of the family.
You can use chips or mulch produced from black walnut in landscaping. However, you should wait two to six months for the chips to compost slightly and break down the juglone chemical before placing the mulch around sensitive plants.