How about algae? I have seedlings in pure milled sphagnum and it greened up almost immediately. I've moved them to a different tank with more circulation, but they were getting a breeze in the other tank as well.
Capensis, Mosser Lee makes a bag of milled sphagnum that I picked up for about $3 at a garden center. Of course, that is the stuff that turned green for me but it is commercially available milled moss.