MACH5, the medium is Stalite, charcoal, and sponge rock. We find most cattleyas LOVE THIS. Our growing conditions in south Florida is natural high humidity, ambient light, and sometimes very hot (currently mid to high 90's during the day). Most organic mediums promote rot growing this way, and we've had great success with this medium. We also have many fans blowing, allowing us to water at least 3X a week, twice with fertilizer., a third to flush.