In a message dated 2/4/08 6:01:49 AM, Barbara Fuhrmann writes:
> what the difference is between Sponge-Rok and perlite.
>
Perlite is small pieces of expanded pumice. Pumice is volcanic glass
(obsidian) which is whipped full of gas bubbles & liquids during an eruption.
When it
hardens it is a solid foam. They say it floats. It certainly floats to the top
of soil mixes. It is durable & is used to aerate potting mixes.
Sponge Rok (sic) is a brand name for coarse perlite. Pieces are generally
1/4" to 1/2." You can buy different grades. I use regular perlite, washed in a
colander, in my fine mix for small orchids, and Sponge Rok in my Cattleya/Phal
mix.
Iris
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