Black Walnut + Highbush Blueberry

Black walnut and highbush blueberry are incompatible in any practical planting scheme. Black walnut roots and decomposing hulls release juglone (5-hydroxy-1,4-naphthoquinone), a compound that inhibits cellular respiration in susceptible plants. Highbush blueberry ranks among the most juglone-sensitive woody plants; exposure causes wilting, chlorosis, and progressive decline that often proves fatal within a single growing season.

The minimum safe distance is 80 feet from the walnut's trunk, though the effective root zone can extend further in sandy or loamy soils. Proximity to walnut stumps carries the same risk, since decomposing roots continue releasing juglone for years. Raised beds with imported soil do not reliably solve the problem if walnut roots penetrate the bed from below.

This pairing offers no useful benefit in any zone or configuration. Site blueberries well away from existing black walnuts, and avoid planting walnuts where blueberries are established.