Carol, I use the MSU type fertilizer since I use RO water on the orchids. But again, it doesn't get a lot of fertilizer; most of the time it's just plain RO water (although I guess that I "cheat" a little in the summer by periodically spraying the orchids with the hose when I'm watering the perennials, which probably gives them a bit more calcium during the growing season, plus whatever else--good or bad--is in the tap).