orchids rely on a medium which is mostly rocks, pebbles, peat moss, and some vermiculite type aerators. I've personally not heard of using just vemiculite but one hint I learned from an elderly japanese woman in Hawaii who raised and sold beautiful orchids at the swap meet every weekend....they love dried, crumbled egg shells around the roots. She told me this promotes blooming more often, and if you know orchids...it is a challenge to get their blooming cycle expedited. The egg shells worked so well I now use them in all my blooming houseplants. Can't remember the last time I threw out an egg shell. Good luck and Aloha!