Unit 3 (003)
1. Black Walnut Toxicity
Some plants will not grow well under black walnut (Juglans nigra) roots. The
toxicity is not well studied, but one study at MSU showed that there had to be a
root to root contact between the walnut and the affected plants. For example,
tomato plants will wilt down on one side. Some authors indicate that the juice from
the fruit husk or leaves will cause the toxicity; I’m not sure that this is true.
2. Age of fruiting
Walnuts (Juglans) and Hickories (Carya) may need to grow for many years before
producing fruit. Some walnuts may need 10 or 15 years before producing fruit.