Busy shredding a huge mountain of leaves to use as mulch and mostly in a
huge compost pile. There are a few English Walnut leaves. Now, somewhere I
either read or heard that Black Walnut leaves were toxic to garden plants
and shouldn't be used for either mulch or in compost. Is that true? Or is
the English Walnut a baddie too?
The roots of Black Walnut ( Juglans nigra L.) and Butternut ( Juglans
cinerea L.) produce a substance known as juglone
(5-hydroxy-alphanapthaquinone). Persian (English or Carpathian) walnut
trees are sometimes grafted onto black walnut rootstocks. Many plants
such as tomato, potato, blackberry, blueberry, azalea, mountain laurel,
rhododendron, red pine and apple may be injured or killed within one to
two months of growth within the root zone of these trees. The toxic zone
from a mature tree occurs on average in a 50 to 60 foot radius from the
trunk, but can be up to 80 feet. The area affected extends outward each
year as a tree enlarges. Young trees two to eight feet high can have a
root diameter twice the height of the top of the tree, with susceptible
plants dead within the root zone and dying at the margins. The juglone
toxin occurs in the leaves, bark and wood of walnut, but these contain
lower concentrations than in the roots. Juglone is poorly soluble in
water and does not move very far in the soil. [from Ohio State
University Extension Fact Sheet HYG-1148-93 by Richard C. Funt and Jane
The Ohio State University Extension and the American Horticultural
Society have reported that R. nudiflorum, Pinxterbloom Azalea, and
Exbury Azaleas Gibraltar and Balzac will grow near Black Walnut and
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Visit my Rhododendron and Azalea web pages at:
I bring back leaves from all over the neighborhood, which inevitably includes
some black walnut leaves. I've never had any problems. It's my understanding
that the roots release juglone. I suspect that the leaves contain minimal
(if any). I useThe leaves for mulch as well as composting.
Pat in Plymouth MI ('someplace.net' is comcast)
Any technology distinguishable from magic is insufficiently advanced.
All parts of black walnut trees contain juglone and can cause problems.
The highest concentration is in the roots and the soil near the roots.
You are probably not getting many black walnut leaves. My experience in
Pennsylvania is that the black walnuts are the first to shed their
leaves, much earlier than any other trees. By the end of summer most
walnut leaves have fallen. Then come down over a long period of time.
When the main mass of other leaves fall, the black walnut leaves are
gone, either from mowing and being mulched or have blown away.
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