Alright guys, Im gonna chime in.
Miracle grow and other cheap synthetic ferts are bad for one big reason, their synthetic.... Which means your soil doesn't truely retain the nutrients, instead in leaches out. It is made from oil. It creates an "addiction" for your plants, meaning they can get to a point where they need it to continue growing strong after a couple weeks. They can jack up your Ph. Very easy to cause nute burn. And the list can go on.
Unfortunatly many people live in locations where the only soil they can get is from wally world, or home depot which only sell MG and Jungle growth. I use to love Jungle growth, but now they add time release as well. So I too am stuck with MG soil, but I use the organic brand. My input on it....
The soil is decent and moderatly loamy, but per 2 gal pot I still add 4.5 cups of vermiculite. Due to one of its primary ingrediants being peat moss it is very acidic, so I have to add 3 tblspn of dolmite lime (regulates Ph to 6-7) to the 2 gal mixture as well. Also I HATE the ferts, I wish I could remove them. When I lived out in the country I found the best soil was just by mixing lake silt, FL dirt (60% sand, 40% soil), composted manure, and some vermiculite with limestone mixed in, it was only at that time did I have no problems (nute burn, Ph, toxic salt build up).
Anyways I've rambled too long and want 2 go to bed. Final point, if you can aquire foxfarm, do it.... MG SUCKS