Best Cat Grass + Growing Medium?

I forgot to post about this earlier, so I'll ask now The first grass we grew was a kit, the one from SmartyKat. I think it was wheat grass. The stuff the kitties have now is a cat grass mix, with a mix of vermiculite and peat moss. I saw one kit product that used only vermiculite, and the webpage said it's better than potting soil.

Actually the only potting soil I could find was designed for ornamental use, flowers and such, so I figured if it's not designed to be used with plants that humans are going to eat, it must not be great for cats, either. But then some sites say you can use any potting soil to grow cat grass in.

What sorts of grass does everyone else use, and what do they grow it in? I know for seeds, "organic" is preferable, but what about growing medium? Is peat moss good? If it says it's sterile, and has no diseases, fungus, or weeds, is that good enough, or should I look for other things as well? The vermiculite said asbestos-free Does vermiculite often have asbestos?

So many questions... But my previous experiences with plants were pretty much limited to mowing the lawn and messing up my mom's garden when I was a kid. Thx for any replies ^^

I use whatever potting soild is the cheapest and I have never had a problem. I use a mix of wheat and oat grass which I bought at the feed store - tons cheaper than in the pet store.