I think it should be undersood that there is MirGro potting soil -------- and there is MirGro Potting Mix.
Potting Mix is sterile. This is why plants of any kind survive much better with it. And to take it up another knotch, we here in Fla have "Bushel Stop"; they have a special potting mix that allows max drainage and the right nutrients to keep the pups moving well along past the sword stage. I have tried Mg soil, Mg mix, native dirt (lots of sand and muckage), all peat moss - but let me tell ya -- the Bush Stop mix of sand, peatmoss, manure, bark chips, "secret dirt" tops them all. Max drainage; and in hot weather all you have to do is water more often. The plants don't die -- period.
Dan