Understanding Fertilizer Labels

Question: What do the three numbers on fertilizer packages mean? For example, 10-10-10.

Answer: The three numbers refer to the percentage of nitrogen (N), phosphorous (P), and potassium (K) in the fertilizer. These 3 elements are referred to as macronutrients because plants need them in fairly large (i.e., macro) amounts to thrive. Plants also need many micronutrients, but in much smaller quantities. While synthetic fertilizers often contain just N, P, and K, organic ones, such as fish emulsions and seaweed extracts, contain numerous micronutrients, too.