“I have several black walnut trees in my yard. Would it be alright to use the leaves in the compost? Question from Raymond of Holt, Michigan
Answer: I would not recommend it. As you surely know, black walnut trees (Juglans nigra) excrete the toxin, juglone, which is deadly to quite a few ornamental plants. The toxin helps reduce competition, making black walnuts bad trees for small home landscapes. Who wants a deadly tree around? Still, black walnuts are beautiful and have edible nuts that feed wildlife, so they are best reserved for more wild areas or fencelines far from the home garden–unless you plant nothing but tolerant plants.
Juglone is largely excreted by the roots, but it is also found in lower quantities in the wood and leaves. The toxin can leach from leaves into compost in small quantities. That’s why you need to be careful about what you plant near a walnut tree and where you put walnut leaves, which are best taken to the woods, fenceline, or bagged for disposal.
Keep in mind that there is no cure once sensitive plants have been significantly impacted by juglone. Exposure signs include yellowing, wilt, stunted growth, and finally death. It may take plants months to die after exposure.
Black Gold Horticulturist
About Jessie Keith
Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.
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