Plants that tolerate black walnut juglone

Black walnut (*Juglans nigra*) produces juglone (5-hydroxy-1,4-naphthoquinone) in all parts of the tree -- roots, leaves, bark, and nuts. Per Penn State Extension, juglone inhibits cellular respiration in susceptible plants, causing wilting, yellowing, and death. The affected zone extends well.

Black walnut (Juglans nigra) produces juglone (5-hydroxy-1,4-naphthoquinone) in all parts of the tree — roots, leaves, bark, and nuts. Per Penn State Extension, juglone inhibits cellular respiration in susceptible plants, causing wilting, yellowing, and death. The affected zone extends well beyond the visible canopy: Penn State documents juglone-affected soil 50–80 feet from the trunk, though concentrations are highest within the drip line (roughly the extent of the canopy).

This is not an obscure problem. Black walnut is a native tree common throughout the eastern US, valued for timber and nuts. Many residential landscapes include mature specimens. The list below is sourced primarily from Penn State Extension's documented juglone tolerance research, supplemented by Cornell and Purdue findings.

The zone of concern

Per Penn State Extension, the highest juglone concentrations occur within the tree's drip line (beneath the canopy). The root zone extends 1.5–3× the canopy radius. Decomposing walnut leaves, hulls, and roots in the soil maintain juglone levels for several years after a walnut tree is removed. Per Penn State, wait 2–3 years after removal before planting sensitive species in the former walnut zone.

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