> Perlite and vermiculite are non-biodegradable minerals(?) which
> are mixed with potting media to provide better aeration. A
> visual inspection leads me to believe that vermiculite is
> derived from mica, but this is conjecture. Perlite, I've
> heard, is some sort of volcanic ash.
> One big Nepenthes grower told me that he doesn't use
> perlite because it can release fluorides (and other
> trace compounds) into the medium. This might not be
> a problem if you repot your plants every year or two.
> I don't know for sure.
Ok, Here's the skinny on them:
Perlite, is in my opinion, the best thing you can do for your
plants. It gives airation and granulation to any soil. I've
not heard about this fluoride poisonning before today so I
can't comment; but what are syptoms of this? Perlite is totally
devoid of any chemical activity (at least the stuff w/out the
fluorides, that is). Perlite lasts indefinitely.
Vermiculite, on the other hand, is very chemically active, unlike
popular misconception. It comes from a mineral very much like mica,
and is made of many, many layers. It is in these layers that nutrients
stick. It comes with nutrients already in it. These are cations
like Ca++, now these are NOT coming from the break down of the
vermiculite, instead it acts like a sponge and soaks them up and
releases them later. I'm using vermiculite only in soil for
Sarracenia seedlings as fertilizer. It causes them to grow very
fast; so fast that seeds sown in october now looks like 2-3 year
old plants! On the down side I planted the RED VFT seedlings in
it and they quickly died. Anyways, vermiculite works best in
drier soil because the wetter it is kept the faster it collapses
and becomes a detriment to the soil. It can last up to one or two
years in good 'dry' condition.
Dave Evans