Fertilizers are used to get elements that plants need into the soil when the natural environment doesn’t provide sufficient quantities. The typical elements are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). They’re actually labelled by the elements they contain. Next time you’re at a garden store, look for “NPK” or “NPKS” on a bag of fertilizer. The numbers after these codes tell you the weight percent of these elements in the bag.