I have a big bag of this porous volcanic rock, which we use in our outdoor vegtable garden. I have read would be good for using in a humidity chamber.. The problem is, it is miracle grow brand and not just plain organic. If i used this, I would assume the mushrooms would absorb the added fertilizer (I've read about mushrooms concentrating and absorbing chemicals). If I set a sheet of plastic down on top of the layer, it would seem harder for the mushroom spawn to absorb this stuff.
I figure I should just get some organic stuff if I even use it but the hardware store only carries the "miracle grow" brand. It says "non-toxic" on the bag but I still dont like the idea of eating a mushroom that is loaded with miracle grow... what do you think?
