Black Walnut bark has been used as a vermifuge for centuries in Asia. It's used as a cure for atheletes foot , and the nuts are delicious, particularly once they've cured for a month to 6 weeks. Walnuts are also a real pain in the garden, because they emit a toxic substance which hinders the growth of other plants. The roots of the black walnut contain a chemical called juglone that kills the roots of other plants that touch the roots of black walnut trees. As well, leaves of the black walnut affect other plants, so conscientious raking is necessary.
Some people say rain dripping from the crown and dropline of the tree also affects plants around it.
The chemical can take several years to kill a succeptible plant. Among landscape plants, evergreens are most susceptible to juglone. The roots of the black walnut extend beyond the tips of the outermost branches. For this reason, many gardens with black walnut trees have very little growing beneath them. I have a large black walnut tree in my garden, so I've been researching this subject quite alot.