Volcanic Rock:

There are two type of Volcanic Rocks that are predominantly used with orchids.

1. Scoria or “Lava rock”:

Scoria (means waste) is a textural rock type formed from lava rich volatiles and Gases. It is a porous rock that retains moisture, has good aeration and is heavy. Scoria exists in various colors (green, brown and black are the most common colors). It is crushed and screened to size for further use. Very useful medium. However, using porous rocks in a potting mix, may create problems with re-potting. Roots of many orchids are capable of penetrating cracks and holes. When this occurs, the roots are anchored and therefore difficult to remove with out causing root injuries. Some orchid plants, like dendrobiums, Vandas etc, do not tolerate root injuries and may die after re-potting.

2. Pumice:

It is a mostly white Volcanic glass that is high in Al-Si content. Very similar to perlite but unlike perlite it is a natural product. It has a higher density, a lower moisture-holding capacity and contains more Na, K and Ca.