Plants need several types of nutrients. Macronutrients are necessary in large quantities. Those that may not be easily available in soil in the right amount are the primary nutrients you find in fertilizer:
Secondary nutrients — oxygen, carbon, hydrogen, calcium, magnesium and sulfur — are also necessary macronutrients but are often available in soil or air. Micronutrients — including boron, chlorine, cobalt, copper, iron, manganese, molybdenum, nickel and zinc — are needed only in small amounts.
Before you shop for fertilizer, perform a soil test. You can purchase a home test kit, or send a soil sample to your local cooperative extension office for testing. The results will tell you what to add to the soil to make it ideal for the plants you plan to grow.
Three prominent numbers on a fertilizer package — known as the NPK value, guaranteed analysis or fertilizer grade — tell you the percentage of available primary macronutrients by weight in the package:
Granular fertilizers deliver food to a plant slowly but have the advantage of longevity.
Broadcast application
This method, which covers large areas well, is used to apply granular fertilizers to lawns or to new beds before they are planted. The broadcast method can be done with a hand-rotary or drop spreader.
Top-dress application
This technique, which provides nutrients to individual plants such as shrubs and perennials, is done by hand with granular fertilizers. Simply apply the fertilizer around the base of the plant, extending to the drip line. For vegetables, place the fertilizer in a strip parallel to the planting row.