I had good results using Mater Magic from the Dynamite guys, available off amazon for less $$ than buying at a box store. It's a pelleted, timed release product so I don't have to remember to apply it every couple of weeks like you do with a water soluble product. I put it in the soil of my Earth Boxes when I planted the transplants, and applied it again about 6 weeks in, early January, I think.
