A good many commercial potting soils are soilless mixes that contain minimal plant nutrients, so supplemental fertilizing is a must, specially for annuals and vegetables. Also the frequent watering most container plantings require will continue to leach out any nutrients that must be replaced if the plants are to thrive under what are essentially cramped, nutrient-poor conditions. The addition of a slow release fertilizer at planting time (like Osmocote) will help but even with this type of product, a water soluble fertilizer applied periodically during the growing season will be of benefit.

What you use is up to you - Miracle Gro in any of its permutations, Schultz, Peters, fish emulsion or some other organic liquid fert - it will all achieve the same purpose.

Thanks alot! I plan on using my bloom builder from last year which is water soluble.