permaculture

[Mark <mpludwig@facstaff.wisc.edu>]

> Date: Sat, 30 Nov 2002 18:52:04 -0600
> From: Lucky Pittman <Lucky.Pittman@murraystate.edu>
> Subject: Re: [grazersedge] Re: Killer oak trees/walnuts
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>
> > > Walnut trees are another tough cookie.   Nothing grows under a
> >walnut tree,
> > > not even grasses because that juice from the shell surrounding the
> >nut is
> > > apparently toxic to competitors.   And even when that walnut tree
> >is cut
> > > and removed, that toxin remains in the soil for years, and nothing
> >grows.
>
> Now y'all are talking about something I know a little bit about.  Many of
> my friends call me Dr. Nutman(I think it's because of my passion for nut
> trees ;>)
> Eastern Black Walnut, J.nigra, does produce juglone - as do the other
> members of the walnut family - and the hickories, as well.  However, none
> of the others, with the possible exception of shagbark hickory produce
> enough of this compound to exert much in the way of an allelopathic
> effect.  Juglone is produced by the roots, and is also present in the
> leaves and nut husks, and even after the tree is cut, it may remain in the
> vicinity of the rootzone for a few years before it all dissipates/leaches 
> away.
> There are a number of plants which have been shown to be susceptible to
> juglone toxicity, but most are ornamental plants and garden
> vegetables.   In most instances, however, the inability of folks to 'grow
> things' under a big black walnut is because that big old tree, with its
> extensive root system is better able to outcompete those underplantings for
> available nutrients and water.  Shading also plays something of a role, but
> since BW is usually one of the last trees to leaf out in spring and one of
> the first to lose them in the fall, it's less a factor than with a large
> maple or oak, but certainly factors into the equation.
> I've never noticed any real problems with grass growing under - in fact,
> right up to the trunk - of a big old open-grown BW out in a pasture.
>
> Lucky
>
>
>
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Mark P. Ludwig
Poultry Research Lab
University of Wisconsin -Madison
608-262-1730 WK
608-846-7125 HM