Final answer:
Fertilizers typically contain three primary macronutrients: Nitrogen for leaf growth, phosphorus for root and flower development, and potassium for stem strength and water regulation in plants.
Step-by-step explanation:
The three ingredients that fertilizers usually contain are Nitrogen, phosphorus, and potassium. These elements are known as the primary macronutrients necessary for plant growth and health. Nitrogen is crucial for leaf growth, phosphorus is important for the development of roots, flowers, seeds, and fruit, and potassium helps with strong stem growth, water movement in plants, and the promotion of flowering and fruiting. While these are the primary macronutrients, fertilizers may also contain secondary macronutrients such as calcium, magnesium, and sulfur, and micronutrients like copper, iron, manganese, molybdenum, zinc, and boron.