I used to pot my ground orchids in a mix consisting of rice husks and perlite. During the dry season, this mix seems fine but in the rainy season, my plants don't look very happy in it.
In my last visit to Chatuchak market in Bangkok, I noticed that the people there had their ground orchids in pure coconut chips (don't know if I got the word correct, what I mean is the 'outter skin' of the nut, not the 'shell', chopped to small square pieces). The plants looked very healthy and produced many flower spikes.
So I decided to re-pot my orchids using 'tree fern roots' (another word which could be mis-used here, but I think you can see clearly in the photos) I also use this medium for my 'air-orchids' such as Cattleya and Brassavola.
This medium retains some moisture and is very airy, so hopefully my plants will like it. The down-side maybe I will need to water more in the dry season.