Black Walnut Toxicity

July 5, 2010 at 1:39 pm Leave a comment

Black Walnut Toxicity

Have you ever wondered why nothing grows under or near a black walnut tree?   The answer is simple– black walnut trees produce a chemical called juglone and this chemical prevents the growth of many plant species.  The chemical is produced mostly in the roots, nut hulls, and buds of the black walnut tree, but it can be found in smaller amounts in the leaves and stems.  Black walnut trees stop the growth of some species of plants because juglone is preventing some species of plants from getting the energy they require to grow.

What are some symptoms of juglone-affected plants? Symptoms can vary from one plant species to another, but the most common ones include stunting of growth, wilting of leaves, and eventual death of the plant.  The toxicity of this chemical should not be overlooked by gardeners as very sensitive plant species can die in as little as two days.

Which species are most susceptible? There is no definitive list of juglone-susceptible plants, but some of the most common species that are susceptible include trees such as red pine and white pine.  Vegetables often affected by juglone include tomatoes and sweet peppers.  Some perennials that are affected by juglone include azaleas and rhododendrons.

What can be done to prevent juglone from affecting your plants?  You can plant garden beds away from black walnut trees to avoid possible damage to susceptible plant species. Removing all plant litter (e.g. leaves, and hulls from nuts) from black walnut trees in the garden bed can minimize the effect on sensitive plants.  Finally, you can choose plant species that are tolerant of juglone and as a result, will thrive near a black walnut.  Some black walnut-tolerant species include perennials such as anemone, lillyturf, jack-in-the-pulpit, mayapple, and Solomon’s seal.  Examples of tolerant tree species include red oak, white oak, and hickory.  If you are interested in learning more about black walnut and black walnut- tolerant plants, please check out the references below.


Connon Nurseries “Plants tolerant to juglone list” Accessed on June 15, 2010.

Martin J., and R.C Funt, Ohio State University, “ Black Walnut Toxicity to Plants, Humans, and Horses” Accessed on June 15, 2010

OMAFRA    “ Walnut Toxicity” Accessed on June 15, 2010

Toronto Botanical Garden “ Juglone and Black walnut (Juglans nigra L.)” Accessed on June 15, 2010


Entry filed under: Trees. Tags: , , .

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