The next stop on our path towards total fertilizer enlightenment is the wonderful world of Greensand.  As we learned in part one of our series, all fertilizers are rated by their NPK ratio, which indicates the percentage of Nitrogen-Phosphorous-Potassium in the product. Greensand (0-0-3) is a great source of Potassium and works as a component of a fertilizer mix and as a stand-alone soil amendment.