These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area. Black walnut trees can be attractive trees in the landscape.
Walnuts are also popular with people, squirrels, and wildlife as a food source.
As you may or may not know, however, the black walnut can also be toxic to certain plants growing in the vicinity. Having a walnut tree in your yard certainly does not mean the landscape will be barren. But if problems have occurred for tomatoes or other sensitive plants near a walnut, the tree is in fact the likely source of the problem. Black walnuts and butternut, both Juglans species, contain a chemical known as juglone. Juglone occurs in all parts of the plant, but is most concentrated in the buds, nut hulls, and roots.