The main ingredients in Miracle-Gro soil amendments and fertilizers are nitrogen, phosphorous and potassium. Ingredients vary, depending on the actual Miracle-Gro product. Miracle-Gro is a brand name that applies to a wide variety of home gardening products.
Nitrogen, phosphorous and potassium are the main nutrients that plants need to grow. Nitrogen helps plants to create new tissue and grow more quickly; and, plants have adapted over time to take up nitrogen quickly, as it is a relatively scarce nutrient in the soil. Most Miracle-Gro fertilizer products use nitrogen as the main ingredient to spur fast growth. Phosphorous is also added to stimulate and strengthen root growth of plants, and potassium is added to strengthen plants and help them with disease resistance.