Black Walnut Allelopathy: Juglone-Sensitive and Tolerant Plants for Your Landscape

Black Walnut Allelopathy: Juglone-Sensitive and Tolerant Plants for Your Landscape

Black walnut roots, husks, leaves, and bark release juglone, a chemical that inhibits many plants (allelopathy). Even decaying roots can affect nearby plants for years after tree removal. Do not use walnut leaves, bark, or wood chips as mulch.

Plants Sensitive to Juglone

Cabbage, Eggplant, Pepper, Potato, Tomato, Apple, Blackberry, Blueberry, Azalea, White Birch, Crabapple, Hackberry, Amur Honeysuckle, Lilac, Saucer Magnolia, Silver Maple, Mountain Laurel, Loblolly Pine, Scotch Pine, White Pine, Privet, Rhododendron, Autumn Crocus (Colchicum), Peony.

Plants Tolerant of Juglone

Lima Bean, Snap Bean, Beet, Corn, Onions, Cherry; Black Raspberry, Red Cedar, Crabapple, Elm, Forsythia, Hawthorn, Hemlock, Hickory, Black Locust, most Maples, Oak, Autumn Olive, Pachysandra, Pawpaw, Persimmon, Sycamore, most Viburnums, Virginia Creeper, Bluebells, Kentucky Bluegrass, Daffodil, Daylily, Ferns, Fescue, Iris, Jack-in-the-Pulpit, Liriope, Narcissus, Phlox, Poison Ivy, Shasta Daisy, Trillium.

Gardener's Note (Anne K.)

Southern Magnolia listed as sensitive, but a 30-year-old magnolia thrives under a 60-foot black walnut in heavy shade. Dogwoods and oaks also do well. However, 'Autumn Blaze' and 'October Glory' red maples died near walnuts; Sugar Maple may be tolerant. The magnolia is extremely full despite dense shade—a great screening plant where space allows.

See also: Walnut Toxicity