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Hyacinth Plant

Q.mulched leaves from an African Sumac Tree

Anonymous added on November 30, 2014 | Answered

We mulched our new flower bed with leaves from our African sumac tree. The petunias are all dying. Are the African sumac leaves poisonous? If so, how long do I have to wait before I can plant in the area again? What can I do?

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Answered on December 1, 2014

I could not find African sumac listed in any of the allelopathic lists, although sumac as a genus is listed. So it's possible. Petunias are also quite susceptible to juglone ( the poisonous compound in allelopathic plants.) The poisonous compounds of black walnut (the most famous allelopathic tree) are supposed to be rendered inert after a month of hot composting, but some people say it may take a year for all the poisonous substances to be gone from the soil. Unfortunately there's not a lot of research on this subject.
Here is an article that goes over some possible problems with petunias: https://www.gardeningknowhow.com/ornamental/flowers/petunia/problems-with-petunias.htm

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