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The posts by Ray Barklow and Iris
illustrate what I meant by the persistence of orchid cultural myths which
are contradicted by Physics and Chemistry.
Iris, despite what you've read,
charcoal absorbs only materials that have unsaturated electron systems,
technically termed "Pi electrons." Common salts are NOT absorbed by
charcoal even though it is very efficient in absorbing [more technically,
"adsorbing"] noxious gases and colored organic
molecules. Charcoal lacks the replaceable ions that make
zeolites capable of exchanging one small inorganic ion for another. Ray is
correct, the more highly the charcoal is activated, the more efficiently it
adsorbs whatever it is capable of adsorbing, but not mineral
salts.
Ray submitted to me, off the OGD Forum, one
of those contrived scenarios that I referred to in my last post, to wit, that
charcoal physically occludes fertilizer solution that precipitates when the
medium surface dries out and is re-released, in presumably concentrated form,
during the next fertilizer application, without the two year delay
implied by Iris. This scenario requires no waterings between fertilizer
applications and never flushing, an extremely bad and fortunately
rare cultural practice, that will cause problems regardless of what
medium is used.
I do not submit this post, just to be
pedantic. Growers in search of the solution to a cultural problem usually
have a real problem. I just want to suggest that they consider other less
remote possibilities than the medium, diatomite, charcoal or
whatever, injuring the roots by concentrating fertilizer
salts.
Bert
Pressman
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