Juglone, a chemical present in all parts of a black walnut tree, is toxic to some plants.
A selection of plants that are not harmed by juglone include:
lima beans, snap beans, beets, corn, onions, parsnips
bluebells, daffodil, daylily, ferns, iris, Jack-in-the-pulpit, liriope, phlox, shasta daisy, and trillium
It is possible to garden under a walnut tree and enjoy greater plant diversity with the use of raised beds. Care must be taken to ensure that the walnut tree roots do not grow into the raised beds and promptly remove all leaves, stems, and fruit that fall into the raised beds.