On Tue, 27 Sep 2005 19:48:17 -0400, "no(SPAM)vasys"
wrote:

Dan wrote:

Hey, hold on a minnit there. I thought one had to be pretty careful about
which wood chips you were putting on the plants cause some trees, like
Walnut, were Bad Things to put on your soil. Do you worry about that?

Dan

Yep.

"Black walnut and allelopathy

Though grown primarily for its wood and nuts, black walnuts are often
found growing on landscape sites where they serve primarily as shade
trees. When certain other landscape plants are planted near or under
this shade tree they tend to yellow, wilt, and die. This decline occurs
because the walnut tree produces a non-toxic, colorless, chemical called
hydrojuglone. Hydrojuglone is found in leaves, stems, fruit hulls, inner
bark and roots. When exposed to air or soil compounds, hydrojuglone is
oxidized into the allelochemical juglone, which is highly toxic.

Several related trees such as English walnut, hickories and pecan also
produce juglone, but in smaller amounts compared to black walnut.
Juglone is one of many plant-produced chemicals that can harm other
plants in a process known as allelopathy. (Additional common landscape
trees with allelopathic properties: sugar maple, tree-of-heaven,
hackberries, southern waxmyrtle, American sycamore, cottonwood, black
cherry, red oak, black locust, sassafrass, and American elm.)"

and

"Reducing allelopathic effects

* Regularly clean up all fallen leaves and fruit from the black walnut
tree, keeping debris away from desired landscape plants.

* Compost plant debris to degrade any toxins present in the compost
pile, and to detoxify the compost. If composting is impractical, do not
use any part of the walnut tree as compost or mulch for other plants. "

See:

http://www.ext.vt.edu/pubs/nursery/430-021/430-021.html

Interestingly my sister has a black walnut on her property that has a
maple tree growing out of a small hole in the crotch of the tree.
Granted the maple has been growing there for at least 3 or 4 years and
is still about the size of (or maybe smaller than) a 1 year old
sapling, but it grew naturally from a seed that fell into a rotted
spot on the walnut tree, and the walnut has yet to be able to kill the
maple.

Dave Hall