Date: Wed, 23 Apr 1997 07:24:19 -0400 (EDT) From: Perry Malouf <pmalouf@access.digex.net> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1607$foo@default> Subject: Re: perlite, vermiculite?
Niels Asger Nielsen wrote:
> I have an English dictionary but perlite and vermiculite are not there.
> Could someone explain to me what it is. I understand that it is used for
> making soil with good drainage. ....
Yes, perlite and vermiculite are added to growing media in order
to improve drainage and to increase porosity.
This listserver had a good discussion of what these are,
exactly; perhaps it was last year sometime. The archives
would contain the complete information.
I'll summarize my understanding. Perlite consists of small white
granules derived from volcanic ash. The granules float
in water, and seem to be inert. They don't rot or break
down. Some people have reported that perlite can contain
traces of fluorides or other salts which might not be
good for plants. I've used it in my Nepenthes mix with
no apparent ill effect.
Vermiculite comes in small chunks. Its color varies
around brown, tan, almost metallic. I've forgotten the
exact mineral classification, but it looks very much
like mica. You can peel away the individual mineral
layers of the larger chunks, just like you can for
mica. If you squeeze a chunk between your fingers
so that the layers are pressed together, you get
a mica flake. Because vermiculite can soak up
water, it does not float as easily as perlite. It
holds water longer. I haven't heard reports of
vermiculite containing leachable salts which might
be harmful to plants.
Regards,
Perry Malouf
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