Walnut tree

Please see the links below for Extension publications that list plants that will not be harmed by juglone the toxic substance that walnut tree roots give off. Since tree roots can extend about 1.5 times the length of the branches it is important to utilize plants that are not damaged by juglone in this area.
https://hort.uwex.edu/articles/black-walnut-toxicity/

http://extension.psu.edu/plants/gardening/fact-sheets/trees-shrubs/landscaping-and-gardening-around-...