Plant nutrients are classified as either macronutrients or micronutrients, depending on the amount of each element the plant needs.
There are six recognized macronutrients - nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. Common micronutrients include boron, carbon, chlorine, copper, hydrogen, iron, manganese, molybdenum, nickel, oxygen and zinc.
Contrary to what their name suggests, micronutrients are no less important to plant health. The only difference between macronutrients and micronutrients are the amounts of each found in the plant tissue.