What plants are sensitive to the juglone produced by black walnuts?
Juglone is a chemical that inhibits the growth of certain plant species. When plants produce a chemical that prevents the growth of other plants, it is called allelopathy. Black Walnut is a common woodland and landscape tree in the Midwest that produces juglone which causes an allelopathic response (inhibition of growth) in other plants.
Not all plants are sensitive to juglone. Members of the tomato family (tomato, potato, eggplant, pepper) are highly sensitive to juglone. Some shrubs like lilac, hydrangea, rhododendron, viburnum, and yew are also considered somewhat sensitive to juglone. There are many other plants, however, that are not impacted by juglone. Shade loving perennials like bugleweed and bleeding heart can coexist nicely underneath walnuts without any injury. It is also important to note that many turfgrass species are tolerant of juglone. They, like many other sun-loving plants, are more likely to perform poorly because of the shade of the walnut tree rather than the juglone.
The degree of symptoms varies with species. Tomatoes are highly sensitive so they often yellow, grow poorly or look stunted, and eventually die when grown near walnuts. Plants that are not as sensitive may yellow slightly or grow more slowly, but are rarely killed. And plants that are tolerant to juglone grow well with no signs or symptoms of injury.
A list of some of the sensitive and tolerant species to juglone are listed below. It is important to note that there are no definitive lists and very few official studies on the impact of juglone on different plant species. The plants listed below have been observed to grow well or not grow well when near black walnuts in a landscape or woodland setting.
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Sensitive to Juglone |
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Tolerant to Juglone |
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Trees |
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Alder |
Alnus glutinosa |
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Buckeye |
Aesculus species |
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Apple/Crabapple |
Malus species |
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Birch (some) |
Betula species |
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White Birch |
Betula papyrifera |
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Catalpa |
Catalpa species |
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Linden |
Tilia americana |
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Dogwood |
Cornus species |
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Hackberry |
Celtis species |
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Hawthorn |
Crateagus species |
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Larch |
Larix |
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Hornbeam |
Carpinus caroliniana |
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Magnolia |
Magnolia x soulangiana |
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Honey-locust |
Gleditsia triacanthos |
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Silver Maple |
Acer saccharinum |
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Maple (most) |
Acer species |
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Norway Spruce |
Picea abies |
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Mulberry |
Morus species |
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Pine (most) |
Pinus species |
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Redbud |
Cercis canadensis |
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Sycamore |
Platanus occidentalis |
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Oak (most) |
Quercus species |
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Willow (most) |
Salix species |
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Sensitive to Juglone |
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Tolerant to Juglone |
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Shrubs |
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Azalea/Rhododendron |
Rhododendron species |
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Arborvitae |
Thuja species |
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Chokeberry |
Aronia arbutifolia |
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Barberry |
Berberis species |
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Cotoneaster |
Cotoneaster species |
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Beauty bush |
Kolkwitzia amabilis |
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Hydrangea |
Hydrangea species |
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Daphne |
Daphne species |
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Lilac |
Syringa species |
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Dogwood |
Cornus species |
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Viburnum (some) |
Viburnum species |
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Elderberry |
Sambucus species |
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Yew |
Taxus species |
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Fringe tree |
Chionanthus virginicus |
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Forsythia |
Rosythia |
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Juniper |
Juniperus species |
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Mockorange |
Philadelphus species |
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Rose of Sharon |
Hibiscus syricacus |
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Serviceberry |
Amelanchier species |
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Sumac |
Rhus species |
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Sensitive to Juglone |
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Tolerant to Juglone |
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Annuals, Perennials and Bulbs |
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Autumn crocus |
Colchicum species |
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Aster |
Symphortrichum species |
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Columbine |
Aquilegia species |
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Astilbe |
Astilbe species |
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Daffodil (some) |
Narcissus species |
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Begonia (most) |
Begonia species |
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Flowering Tobacco |
Nicotiana species |
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Bugleweed |
Ajuga species |
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Lily |
Lilium species |
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Bleeding heart |
Lamprocapnos spectabilis |
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Peony (some) |
Peaonia species |
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Cranesbill |
Geranium species |
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Petunia |
Petunia species |
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Daylily |
Hemerocallis species |
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Ferns (many) |
various genera |
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Hyacinth |
Hyacinthus |
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Iris (many) |
Iris species |
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Phlox |
Phlox species |
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Stonecrop |
Sedum species |
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Tulip (some) |
Tulipa species |
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Sensitive to Juglone |
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Tolerant to Juglone |
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Fruits |
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Apple |
Malus domestica |
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Black Raspberry |
Rubus occidentalus |
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Blackberry |
Rubus species |
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Cherry |
Prunus avium |
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Blueberry |
Vaccinium speices |
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Peach |
Prunus persica |
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Grape |
Vitus species |
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Plum |
Prunus domestica |
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Pear |
Pyrus species |
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Sensitive to Juglone |
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Tolerant to Juglone |
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Vegetables |
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Asparagus |
Asparagus officinalis |
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Beans |
Phaseolus species |
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Cabbage |
Brassica oleracea |
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Beets |
Beta vulgaris |
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Cucumber |
Cucumis sativus |
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Carrots |
Daucus carota |
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Eggplant |
Solanum melongena |
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Corn |
Zea mays |
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Pepper |
Capsicum annuum |
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Melons |
Citrullus species |
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Potato |
Solanum tuberosum |
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Onions |
Allium cepa |
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Rhubarb |
Rheum rhabarbarum |
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Squash |
Curcurbita species |
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Tomato |
Lycopersican esculentum |
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