FAQ: Meaning of NPK 

Q: What do the three numbers next to NPK on fertilizer packages mean?


A: Those numbers refer to nitrogen (N), phosphorous (P), and potassium (K), respectively. Like us, plants need nutrients to be healthy and strong. Nitrogen helps plants build chlorophyll, which helps them use sunlight to turn water and carbon dioxide into sugars that feed the plant. You can tell if a plant isn’t getting enough nitrogen if its leaves look yellow or pale green. Symptoms usually appear on the lower leaves first. 
Potassium helps stems and roots develop and gives flowers their rich coloring. Plants that are low on potassium will often have yellow leaves, too, but the yellow starts at the leaf’s edges and works its way in. Phosphorous is important for rapid root growth, so it isn’t always easy to see a deficiency in this nutrient until a plant is clearly stunted.