Most orchids actually don’t need soil to grow, but rather need an airy mix with really good air flow and drainage.

The mixture may consist of:
Fir Bark
Tree Fern
Sphagnum Moss
Perlite
Coco husk chips and/or styrofoam peanuts
Every mix you find in the stores is unique, and you can even mix your own. Horticulturists from the University of Tennessee recommend the following mix:
Fir bark
Perlite
Chopped sphagnum