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.