Kathi, I too am wondering about rock and aggregate media, especially for my more dry tolerant Encyclias. I just created a new post asking for information about a product called Pearl Rock, which I repotted three Encycs into today as an experiement. I saw lava rock but it all appears so large? Can anyone mention the typical size of lava rock, or other aggregates they may be using as a media for their orchids?! Thanks!