Does the MG have Micchorizae. If not you should add some. That seems to be a key thing for me when starting new plants. If I use regular SuperSoil the plants are severly stunted and never catch back up even if I transfer to Happy Frog later on.

I am not an expert either and I don't have experience with MG. I have had great luck with Fox Farms, Roots and Vermiblend.