Each of the three nutrients in the N-P-K has its own special job to do. Nitrogen (N) spurs vigorous, leafy growth and rich green color in lawn grasses and other plants. Phosphorus (P) focuses energy on strong root development and flowers, fruits and seeds, while also helping plants use other nutrients efficiently. Potassium (K) enhances overall growth. It helps regulate root and top growth and keeps plants healthy and balanced.