Mg as in Miracle grow? Even if t is organic, they make it potent and honestly, not all plants are grown the same, not only that but I think that since MG is a product for "other" gardening needs, it might have something that would damage "Weeds". IDK, maybe it's just me o.0... like I keep saying and I'll keep repeating myself, go organic. Go out somewhere into an area where you can dig up some dirt no one will miss. Make sure there is lush green vegetation on it. The darker and finer the dirt, the better!. You can add boiling water to the dirt before using it with your plants to kill damaging bacteria, then again, it will also kill the beneficial bacteria (worm castings and/or earthworms can fix that) . Dirt is dirt unless something has been added to it (like MG), then it's just fertilized dirt and that's bad for seedlings unless the formula is specifically made for cannabis or hops.