On Mon, 09 Jun 2003 11:31:33 GMT, (BroJack)
wrote:

The horticultural books say that the roots of juglans (walnuts)
release a poison that prevents other plants from growing near them.
Nonsense. In 30 years of observing them in my "wild" areas, I haven't
found this to be true.

Does anyone know the origin of this misinformation and why the books
keep repeating it?

It's not misinformation. Some plants are adapted to cope very well with
growth-suppressing hormones or natural-herbicides such as are exuded
chiefly from the roots of such plants as walnuts, many grasses,
dandylions, monkshoods, cherries, & other plants that give themselves an
"edge" by slowing down the growth rate of the plants they compete with.
Other plants are serioiusly retarded or even killed by juglone & other
natural herbicides & growth suppressants. Black walnut has vastly more
juglone than any other tree likely to be encountered, so the effect is
particularly obvious on plants sensitive to juglone (one would rarely see
nightshades or other potato-family plants thriving under a black walnut).

But I'm sure some of the cause of plant deaths under walnuts is the deep
shade & the tree roots drying out the soil very rapidly or the canopy
keeping rain from reaching the ground & autumn leaves falling so thick
they smother what ever almost got established. Yet it all gets blamed on
juglone even where there are multiple causes.

I have some rhododendrons growing inside the dripline of an enormous old
chokecherry such as also exude juglone, though a tiny fraction of what
black walnut produces. These dwarf rhodies & azaleas are doing fine (one
is doing super-fine & seems to LOVE the jugloned soil) but I can tell the
majority under the chokecherry do have some small negative effect on their
growth rate & degree of flowering. If I didn't have many specimens here &
there for comparison I might not notice the juglone effect on those few.

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/