I hate to say this, but I'm probably going to go with the most economical choice.

I've personally never had a major problem with products like Miracle Gro and so on. I almost feel like they DO serve some sort of purpose and that's to grow more food.
When it comes to going green for me, I think energy conversation and things that are not extremely harmful to the planet. Now, Miracle Gro may not be the best option for a clean product to use on plants, but its main purpose is more of a societal one.