The NPK ratio shows how much of Nitrogen, Phosphorus and Potassium content is present in the nutrient. Plants need large amounts of Nitrogen during the early phase, a little less during the mid-level growth and almost none during the late phase. Phosphorus and Potassium are needed in large quantities during the flowering. The NPK Ratio is usually a number like 5-3-4 which indicates how much quantity of each is present in the mix.