mulched leaves from an African Sumac Tree

Question

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?

Answer 1

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.
https://www.gardeningknowhow.com/garden-how-to/info/allelopathic-plants.htm
Here is an article that goes over some possible problems with petunias: https://www.gardeningknowhow.com/ornamental/flowers/petunia/problems-with-petunias.htm