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Black walnut trees can grow up to 100 feet tall and they bear delicious, oily nuts that make for superb chocolate chip cookies. Black walnut wood is prized by furniture and cabinet makers.
But among gardeners black walnuts have a reputation for being unfriendly to other plants. That's because juglone, a compound in black walnut roots, nuts and leaves, has been found to be toxic to some garden plants. But juglone may not be the sole reason why plants close to black walnut trees don't grow well. Most garden crops grow best in full sun and rich, moist soil—just the opposite of conditions you find beneath the canopy of a large, dense tree like a black walnut. If your garden gets full sun, you water it regularly (since those tree roots drink up a lot of moisture) and you keep a half-inch layer of compost on your garden—which mitigates the effects of juglone—you may very well be able to grow some vegetables near a black walnut tree.
In addition, many perennials adapted to dry, shady conditions grow unhampered near black walnut trees. The University of Illinois Extension Service reports that these perennials resist walnut toxicity:
Cranesbills (Geranium spp.)
Daylilies(Hemerocallis spp.)
Leopard's bane (Doronicum spp.)
Lungworts (Pulmonaria spp.)
Trilliums (Trillium spp.)
Sweet woodruff (Galium odoratum)
Flowering bulbs, such as crocuses, daffodils, grape hyacinths, snowdrops, winter aconites, squills, and glory-of-the-snow are resistant to juglone, too.
Larry Hodgson, author of Perennials for Every Purpose, recommends these bloomers for shady spots:
