Pittosporum near black walnuts

Asked August 22, 2019, 4:56 PM EDT

We are considering planting some pittosporum as a privacy hedge in a 50 ft area between 2 old black walnut trees. Would they tolerate 1) the Juglone and 2) the partial shade (about 4 hrs of sun per day)

Santa Cruz County California black walnut tree black walnut allelopathy

1 Response

Hi, I assume you're talking about the alleged "allelopathic" or toxic effects of black walnut trees on nearby vegetation. Fortunately for gardeners, there in no reliable basis in fact for this common belief. Scientists have not been able to reliably show any ill effects from black walnut trees planted in close proximity to other plants in field tests. According to Dr. Linda Chalker-Scott, WSU's myth-buster Garden Professor, the entire conspiracy against black walnuts has been based on two very old Extension publications, one of which has been withdrawn from circulation, and the other doesn't even exist! So as long as your pittosporum is planted in healthy conditions and is properly maintained, it should remain healthy. To read more about the myth of black walnut allelopathy, see: http://cru.cahe.wsu.edu/CEPublications/FS325E/FS325E.pdf If you'd like to see other horticultural myths that Dr. Chalker-Scott has debunked, this makes for fascinating reading: https://puyallup.wsu.edu/lcs/