Companion planting guide › Black walnut and tomatoes (avoid)

Black walnut and tomatoes (avoid): does it work?

Proven Consistent benefit shown in replicated field research or long-running extension trials.

Tomatoes are among the most juglone-sensitive vegetables. Do not plant them in a black walnut root zone.

1. Penn State Extension. Allelopathy in the Home Garden.
2. Ohio State University BYGL. Horticultural Horrors II (black walnut and tomatoes).

Mechanism

Allelopathy: black walnut roots, leaves and hulls release juglone.

What the research found

• Penn State Extension lists tomatoes among the vegetables least tolerant of juglone.
• Ohio State Extension advises not to grow tomatoes within the black walnut root zone, which can extend well beyond the canopy.

Caveats

Raised beds with liners can help but roots may still reach them. Other Solanaceae are also sensitive.