Vitex, like many shrubs, may be susceptible to black walnut's toxicity. Black walnuts naturally produce juglone. Plants within the trees' root or drip zones can be damaged of killed when exposed to the chemical. Vitex is not on any list of plants tolerant of juglone, so black walnut should be considered toxic to the shrub.
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Aileen Clarkson has been an award-winning editor and reporter for more than 20 years, earning three awards from the Society of Professional Journalists. She has worked for several newspapers, including "The Washington Post" and "The Charlotte Observer." Clarkson earned a Bachelor of Arts in journalism from the University of Florida.