re:perlite vs polystyrene

From: NPLUMMER@hg-basic1mail.hg.med.umich.edu
Date: Mon Feb 09 1998 - 16:53:34 PST


Date:          Mon, 9 Feb 1998 19:53:34 -0500
From: NPLUMMER@hg-basic1mail.hg.med.umich.edu
To: cp@opus.hpl.hp.com
Message-Id: <aabcdefg525$foo@default>
Subject:       re:perlite vs polystyrene

Michael Gray <mikeg@dstc.edu.au> asked about perlite vs. polystyrene.

Perlite is porous, so it will wick up some water by capillary action. I
guess that could be good or bad depending on your watering habits.
Perry Malouf has pointed out potential problems with colored
polystyrene. I just wanted to note that in some cases perlite may also
be phytotoxic. On the Orchids List Digest, one well-known slipper
orchid grower reported that his Phragmipedium besseae seedlings suffered
unexplained necrosis at the leaf axils. The perlite in his mix was
tested and proved to be high in fluoride (!) which was apparently
leaching out. When the perlite was removed from the mix, the necrosis
vanished. This particular orchid grower is renowned for the quality of
his plants and his culture.

I haven't had any problems with perlite in orchid and Nepenthes pots, but I
wanted to pass along this potential caveat. Perhaps different batches have
slightly different mineral content?

Nick

----------------------
Nicholas Plummer
nplummer@umich.edu
http://www-personal.umich.edu/~nplummer/



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