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COLUMN: Coping with black walnut toxicity

Denise Miller-Hubbell, Cornell Cooperative Extension Oneida County
Posted 5/7/23

Anyone who has ever tried to garden under or around a black walnut tree (Juglans nigra) has undoubtedly been frustrated.

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COLUMN: Coping with black walnut toxicity


Anyone who has ever tried to garden under or around a black walnut tree (Juglans nigra) has undoubtedly been frustrated. Your black walnut is a valuable shade tree, but you will engage in plant warfare if it overhangs your garden.

Juglone is the culprit! It’s most concentrated in the roots, buds, and nut hulls and, to a lesser degree, in the leaves and stems. Juglone leaks into the soil, acting as a “natural herbicide,” eliminating competition by inhibiting the respiration of nearby susceptible plants. Plants beneath the canopy are most at risk, although the toxic zone of a mature tree could be up to 80 feet from the trunk. The affected area expands as the tree grows. As toxin seeps into the soil, companion plants may show symptoms ranging from stunting, yellowing, and wilting to death. Some plants may survive for years but begin to show symptoms as the tree increases in size.

So, is growing near a black walnut a death sentence? No, but using caution and choosing tolerant plants is the key to success. Transplant-sensitive species should be planted elsewhere. Also, keep the bed free of leaves, hulls, and seedlings.

The following partial list of tolerant plants is based on observation since few plants have been experimentally tested. Any list should be used for guidance but not regarded as definitive.

Trees: Japanese Maple, most maples, Eastern Redbud, Canadian Hemlock, American Beech, Big Leaf Linden, and Black Cherry.

Shrubs and vines: Arborvitae, Barberry, Bittersweet, Rose-of-Sharon, Juniper, Euonymus, Viburnum, Ninebark, Forsythia, Sumac, Clematis, Virginia Creeper, Black Raspberry, Elderberry.

Perennials: Anemones, Aster, Astilbe, Bee Balm, Bellflower, Black Eyed Susan, Bleeding Heart, Bugleweed, Calendula, Cardinal Flower, Coneflower, Coral Bells, Daylily, Dutchman’s Breeches, European Ginger, Ferns, Goat’s beard, Glory-in-the-Snow, Hellebore, Hollyhock, Hostas, Iris, Lambs Ear, Lungwort, Shasta Daisy, Siberian Iris, Solomon’s Seal, Stonecrop, Primrose, and Yarrow.

Vegetables: Beans, Beets, Carrots, Corn, Onions, Parsnips, and Squash.

Annuals: Pansy, Impatiens, Morning Glory, Marigolds, and Zinnias.



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