In many soils, these elements are naturally present in sufficient quantity to meet the needs of trees, shrubs, and other large plants for many years. Still, gardeners often apply additional phosphorus and potassium to the soil when digging new beds, as part of annual care for heavy feeders such as roses, and to encourage the best performance from annual vegetables and flowers. Application near the root zone is easy when you're making a new bed. Secondary Nutrients Calcium, magnesium, and sulfur are also important for plant health. They're largely available to plants through minerals in the soil.
Magnesium forms the core of every chlorophyll molecule.
And sulfur combines with nitrogen in making protoplasm for plant cells. The micronutrients include copper, iron, manganese, zinc, and other trace minerals. Copper and iron are used in chlorophyll formation. Manganese and zinc seem to function as catalysts in the utilization of other nutrients. Micronutrients are usually available to plants through minerals in the soil.