The 14 essential elements (also called essential plant nutrients) are those your plants require in order to grow. The three primary macronutrients are nitrogen, phosphorus and potassium. The three secondary macronutrients are calcium, sulfur and magnesium. The micronutrients (also called trace minerals) are boron, chlorine, manganese, iron, zinc, copper, molybdenum and nickel. Plants also require hydrogen, oxygen and carbon (for a grand total of 17 essential elements), but they obtain these from their environment.