The thing with MG is it is high in NPK and is a slow time release.
If you believe the NPK is too high, you can simply use less.
As to time release, that depends which product you use. Some of the MG fertilizers are slow release; some are water soluble (ie "fast" release).
Again, there are some 15+ products branded as "Miracle Gro" and they're completely different formulations with different NPK ratios, different strengths, different trace elements, etc.
You will need to flush the living crap out of the plants to reduce the harshness. IF you have ever smoked pot that has been grown with MG you know the burning harsh smoke I speak of. There are so many better nutes out there for growing marijuana and you dont need to have a hydroponics supply store near you, that is what the internet is for. Order nutes online. Keep the MG for the flowers. And personally I prefer organic nutes not chemical but that is just me.
Presumably you're going to flush if you use any chemical fertilizers, not just MG.
I think a big reason Miracle Gro is perceived as giving lousy buds is because its the first choice of total newbs, who aren't all that adept at growing anything, let alone timing their harvest, manicuring, and especially curing. These growers would be putting out harsh herb no matter what they did.
Again, I'm not saying Miracle Gro is the best product, and its definitely not. I agree there are better, and I agree organic is the "best". . .if you can do it. I'm saying you can get good results with it, if you pick the right product and know what you're doing with it.
Not incidentally, with two states now fully legal, and inevitably more on the way, its only a question of time before there is actually a Miracle Gro branded formula specifically designed for cannabis. No, they're not going to call it "Miracle grow cannabis", for obvious reasons, but it will have a coded name like "Miracle Grow Herb" and say that its good for growing "herbs and ornamentals", or something like that.
See here:
http://online.wsj.com/article/SB10001424052702304665904576383832249741032.html
There is already are JR Peter's "Jacks" "hydroponic herb" and "bloom booster" formulas that I've "heard" work every bit as well as specialty branded hydroponics products that cost 6x as much.