> ...What exactly are pearlite and vermiculite?
> How do they effect the soil? Do they change soil pH?
> Do they contribute minerals to the soil?
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. I use perlite mixed
with sphagnum for my Nepenthes and the plants grow okay.
I've never experimented with other potting media to see
if the plants would do better.
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.
For my plants, the perlite provides some aeration as the
sphagnum begins to break down.
There are many others who know more about perlite and
vermiculite, and I hope they contribute to this thread.
Perry