The Black Walnut Tree, a large and common deciduous tree, produces more than just edible nuts. The roots, buds, and nut hulls produce a chemical called “Juglone”. According to Purdue University, “Juglone has experimentally been shown to be a respiration inhibitor which deprives sensitive plants of needed energy for metabolic activity”. The toxic zone from a mature tree occurs on average in a 50-60′ radius but can be up to 80′. The following is information about trees that are sensitive and tolerant to Juglone. Note: These are based upon observations and not clinical tests.

Tolerant:

• Japanese Maples
• Southern Catalpa
• Eastern Redbud
• Canadian Hemlock
• Arborvitae
• Sycamore
• Elm
• Red Cedar
• Hawthorn
• Oak

Sensitive:

• White Birch
• Ornamental Cherries
• Red Chokecherry
• Crabapples
• Silver Maple
• Pear
• White Pine
• Norway Spruce
• Apple Tree

For more information on specific varieties that are tolerant/intolerant to Juglone please refer to our sources.

According to the University of Minnesota, “There is no chemical control available to stop the potentially toxic effect of black walnut roots. The only practical control is physical separation. Cutting down and removing the tree is of limited help, unless all roots are removed from the soil. As indicated, black walnut leaves probably give off little juglone. But to be on the safe side, it is best to rake up the leaves, and to avoid using the bark or chips as a mulch.”

Sources: http://www.ces.purdue.edu/extmedia/HO/HO-193.pdf, http://ohioline.osu.edu/hyg-fact/1000/1148.html, http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/h407blkwal-tox.html