I've been using stuff from home depot. I forget the name, but it comes in a yellow bag. its a vegetable and herb garden mix (not potting mix). it's just peat moss, perlite, and dolomite lime. has has a small amount of nutes already in it, but its minimal. then I put it in a plastic tub from wally world and mix in a little organic fertilizer, more lime, perlite, and vermiculite, and add liquid karma to some water and moisten. then let sit for 2-3 weeks and it should work fine. I didn't have any problems with 20 plants.