Juglone Toxicity Info – Resistant and Susceptible Plants

Black walnut (Juglans nigra) and Butternut trees and closely-related species produce a toxic substance, Juglone, which can be harmful to plants growing in areas nearby the trees or their root systems which can be 50’-60’ radius for large trees. Juglone toxicity inhibits respiration in susceptible plants and the effects can include stunted, retarded or deformed growth or death.

The black walnut tree is the most commonly planted tree in the north. At maturity it reaches 80’tall and 50’ wide. Butternut trees also makes a good shade tree and is grown for its edible nuts. At maturity the butternut reaches 65’ in height and also becomes 50’ wide.

Juglone Damage

Damage due to Juglone depends on how close the susceptible plant is growing to roots of the trees. Root proximity appears to be necessary before harm is done to a susceptible plant. It is also possible toxicity could occur from leaf decay, from nut husks and from moisture dripping through the leaves of the trees. The quantity of Juglone produced by these methods is small and less damaging than root contact.

Control Juglone Damage

The best way to control any damage done by Juglone is to avoid planting susceptible plants near Black Walnut trees and closely related species. With the lack of a chemical control for Juglone, using resistant plants in the landscape and keeping susceptible plants with good resistance from the leaf canopy of these trees is the best physical control.

Tree removal is not recommended because removing the roots is complex and any roots remaining in the soil can still give off Juglone until they decay completely which can take several years. Practicing good sanitation of leaves and nut husks is advised. Rake up the leaves and don’t use them in the compost pile. Avoid using the wood or bark as mulch.

Note about Juglone Plant Lists

The resistant and susceptible plants listed here are generally common plants and both lists are not complete as research continues. Often research is based on observations of what plants do best and what plants do not thrive in the presence of Juglone-producing trees. Get the full list of plants resistant or tolerant to Juglone on this downloadable PDF from K-State Research and Extension.

Plants Susceptible to Juglone toxicity

Trees

Alder
Chokeberry
White Birch      
Hackberry
Linden (Basswood)
Magnolia
Pine
Rhododendron
Silver Maple

Evergreens

Norway Pines
Yews

Shrubs

Azalea
Cotoneaster
Hydrangea
Lilac
Potentilla
Privet
Rhododendron
Mountain Laurel

Fruits

Apple
Blackberry
Blueberry
Pear

Vegetables

Cucumbers
Peppers
Potatoes
Squash
Tomatoes