Organic or synthetic? Most of the confusion I see regarding organic fertilizer falls into two groups.
Most questions have to do with trying to understand what the differences are, usually with an underlying question, "Why should I use organic fertilizer?"
The other uncertainty has to do with "What is an organic fertilizer?"
Because most people relate to fertilizing products by brand name, not ingredients, the second question is easier to answer than the first. Brands like Miracle-Gro, Scott's, Vigoro, Best, Osmocote and Shultz are synthetic, not organic, although each of these companies is attempting to enter the growing organic fertilizer marketplace. The most popular organic fertilizer brands are likely Dr. Earth, E.B. Stone, Whitney Farms and Foxfarm.
But the best way to distinguish organics from synthetics is reviewing the ingredients list. Synthetics will include sources like ammonium nitrate, monammonium phosphate, ammonium sulphate, urea, potassium chloride, etc. Organics will be from sources like bone and fish meal, rock phosphate, kelp, alfalfa and soybean, various guanos and so on.