April 14, 2010
The key point to remember when thinking about selecting an appropriate potting medium is quite simply that orchids don't grow in pots or in a pile of bark.  Even those orchid species that do grow ON the ground (not IN the ground) are found growing in very airy leaf litter/debris or the crevices of rocks, which have exceptional drainage and air circulation.  You could pour buckets of water over them and they would dry out very quickly from the excellent air circulation.  This is not the case with our home orchids with their roots trapped in wet mix at the bottom of our pots.  Thus you have now discovered the "Achilles Heel" of indoor orchid growing and the cause of many orchid obituaries past, present and future.

Most orchids are epiphytes, using their roots for attachment to branches and other surfaces, as well as to absorb nutrients.   Yes they like to grow ON stuff. Mounting orchids to plaques of bark or onto a stick can be very appropriate methods, depending on the eventual size of the plant and your conditions.   

So now that you understand that the  number one killer of orchids is root rot.  You may consider using a potting mixture or medium that does not break down.  Bark mixes should be replaced every 12 months when your orchid is just beginning a new growth cycle.  Old bark turns to mush and will be like planting those orchid roots in wet dirt at the bottom of the pot.  One of the methods I find useful is replacing the bark with pumice when I acquire a new plant.  The pumice doesn't break down and the roots don't rot in that case.  Thus the pumice doesn't need replacing.  I'm a lazy orchidist so the less repotting the better.  

If you try a media that doesn't break down such as readily available and inexpensive crushed rock or pumice, you'll find that you don't kill your orchids with root rot.  Not killing your orchid is the first step in learning how to grow them.