The initial NPK represents Nitrogen, Phosphorous, and Potassium. The three letters refer to the chemical symbols used to identify these elements in plant Fertilizer packaging. N for Nitrogen P for Phosphorus and K for potassium.

The numbers on the fertilizer package refer to the NPK ratio, which determines the ratio of Nitrogen, Phosphorus and Potassium in the package. Different plants often have different nutritional requirements. As a result there are many different NPK fertilizer blends available in garden centres.