What Is the Purpose of Fertilizers?

Fertilizers supplement essential nutrients in the soil needed by all plants for healthy, vigorous growth. Contrary to popular belief, fertilizers are not plant food. Plants manufacture their own food from water and carbon dioxide through photosynthesis. Fertilizers instead provide the nutrients plants need to grow. Think of fertilizers as plant vitamins.

All fertilizers contain one or more of the "big three" plant nutrients; nitrogen, phosphorous, and potassium. These nutrients are used by all plants in the largest amounts and most soils lack enough of one or more of these to sustain long-term healthy, vigorous growth, especially under conditions of continuous cultivation, like farming. Fertilizers are labeled with a series of three numbers separated by dashes; 10-12-16. These are the relative percentages, by weight, of each nutrient contained by the fertilizer.

Sulfur, magnesium, and calcium, while used in smaller amounts than the "big three" are still used in relatively large amounts by many plants and are called, along with the "big three" macro nutrients. Other nutrients used by most plants but in much smaller amounts are boron, zinc, copper, molybdenum, chlorine, manganese and iron. These are called micro nutrients. Some types of fertilizers will contain one or more of these other nutrients. They will appear on the label, but separately from the three numbers representing the "big three."

Fertilizers may be organic or inorganic. Organic fertilizers come from entirely natural sources and include seaweed extracts, various animal manures, blood meal, bone meal, fish emulsions, worm castings, and many others. Inorganic fertilizers are those manufactured artificially. Many organic fertilizers naturally contain one or more nutrients other than the "big three" while most inorganic fertilizers contain only one or more of these three main nutrients. Organic fertilizers tend to release their nutrients more slowly than inorganic fertilizers which are formulated for immediate availability of nutrients.

Fertilizers come in an almost infinite variety of formulations. Fertilizers high in nitrogen are used for lawns, golf courses, and farming purposes. Nitrogen promotes strong, vigorous growth of leaves and stems. Phosphorous and potassium promote abundant growth of flowers, fruit and strong root systems. Many plants benefit from a fertilizer high in nitrogen early in the growth cycle, and more phosphorous and potassium later in the cycle as they begin to produce flowers and/or fruit.