The Rural Voice, 2000-08, Page 57which walnuts and pines were
planted in that pattern by the
Ministry, there are as yet no signs of
either species killing the other. But
they were planted only 21 years ago
so there is time yet.
Competition for light and moisture
under the walnut canopy also greatly
affects which species survive, making
it difficult to determine exactly what
kills other plants.
Depth of the roots makes a
difference, too. Walnuts tend to have
deep roots, particularly near the
trunk. Plants near the trunk,
especially those with shallow roots,
are less likely to be affected by the
juglone than those further out where
the walnut roots are nearer the
surface. But researchers at Iowa State
University found, "The greatest
concentration of juglone in the soil
exists within the dripline of the trees.
(The dripline is the ring around the
tree formed by the tips of the
branches.) Plants susceptible to
juglone are occasionally damaged
well beyond the dripline as the roots
of walnuts may extend two to three
times the crown radius. (The distance
from the trunk to the dripline.)"
Even after a walnut tree is
removed, the juglone might remain in'
the soil for several years, although
even this notion is controversial.
Some plant scientists say that one
year is enough for the juglone to
disappear. Others say it takes more
time.
One topic on which they do agree
is that the use of black walnut chips
or sawdust for bedding can cause
acute laminitis in horses — an
inflamation of the hoof. Paddocks or
stables close to walnut trees can also
cause the problem.
But there is a difference of opinion
on how damaging to plants are
walnut sawdust or wood chips used
as mulch in a garden. Some
researchers say that as long as the
material has been composted for
about a year it will do no harm.
Others caution against using it at all.
There seem to be a few points that
all the researchers agree on: •
• Do not plant a walnut tree in an
urban area. It can grow to be huge
and will rob other plants of moisture
and light and, because of the juglone,
will restrict what else you can plant
in your garden.
• Do not use walnut chips for horse
bedding or use an area near a walnut
tree for a horse paddock.
• Do not place walnut chips or
sawdust in a compost pile unless you
plan to wait at least a year before
using it as mulch.
• Avoid planting anything under or
near a black walnut tree that has been
observed to be susceptible to juglone
toxicity, especially if the soil is
poorly drained.
Here is a partial list of plants that
most researchers agree should not be
planted near a black walnut tree:
Vegetables and fruits
Tomato, potato, asparagus,
cabbage, rhubarb, eggplant, pepper,
blackberry, blueberry.
Trees and shrubs
White pine, red pine, Scotch pine,
white birch, basswood, pear, apple
(some), crabapple, silver maple,
Norway spruce, privet, lilac, yew,
mountain laurel.
Flowers
Rhododendron, azalea, potentilla,
hydrangea, honeysuckle,
chrysanthemum (some), peony
(some), petunia, lily, narcissus,
buttercup.
Field crops
Alfalfa, crimson clover, tobacco.
Unfortunately, creeping Charlie,
chickweed, dandelion and hawthorn
do not seem to be affected by
juglone.
Speaking of black walnuts, in the
November 1999 issue of The Rural
Voice, I mentioned that I had tied a
piece of Irish Spring soap to a branch
of each of the walnut saplings in my
plantation (this one was planted in
1994) to see if I could keep the deer
away. Well, it worked. This spring I
found no evidence that deer had been
near the young trees no terminal
buds nibbled off and no bark
shredded by antlers. I plan to do it
again this autumn before the rutting
season begins.0
Andrew Grindlay fauns 100 acres of
trees in Huron County.
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