Juglone and walnut toxicity
You may have heard that you can’t grow anything under or around a walnut tree. Well, there’s some truth to that. The roots, leaves and nuts of several different walnuts and some hickories produce a substance called juglone that inhibits growth of certain plants. Those plants that are susceptible include members of the tomato family, potatoes, blueberries and azaleas.
Luckily, there are many plants that don’t seem to be bothered. Some plants that resist walnut toxicity are European wild ginger, bee balm, spiderwort, Siberian iris and weeping forsythia. A more extensive list of plants can be found at the University of Wisconsin Urban Horticulture Web site: