Toby Hemenway has a theory that mulberry bushes can neutralize juglones, and create a safe space in the “lee side”, but I was never clear if that was by root zone exclusion or some other mechanism. If the former, I’m curious to find out if it works with a new mulberry in the root zone of an old walnut.
>The roots of the black walnut tree emit a chemical known as juglone. This chemical is toxic to many other plants, and can stunt them or kill them in as little as a month. The toxic area around mature black walnut trees is usually a 50- to 60-foot radius around the trunk, but can be as much 80 feet.