I have seen orchids cultivated in bark, perlite, rock wool, moss, peat, expanded clay granules, expanded polystyrene foam granules, coconut husk, broken bricks, broken terracotta pots, perlag (a dense version of perlite), pumice, and granite (yes, granite), dried cow dung, and just plain air (vandas).

And you have to see the orchid roots growing on my aluminium benches and up brick walls!

In addition to that, I have heard of a practice of growing cymbidiums in fresh horse manure.

Some will have you believe that you can only grow orchids in one of the substrates above, while others will swear by a magic mix of these.

I believe that orchids don't actually care what the substrate is, as long as it is inert enough. It depends entirely on how you water them.

Weng