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Plant Nutrition

Ever wonder what those three numbers on fertilizer bags are?


Like humans, plants need food to live and grow. However, plant nutrition is synthesized from the basic elements in their environment and from photosynthesis.


Photosynthesis is a wonderfully complicated event in which green plants use sunlight to synthesize food from carbon dioxide and water. It generally involves the green pigment chlorophyll and to our benefit, generates oxygen as a byproduct. Photosynthesis may be the most important biochemical process we know since nearly all life on earth depends on it.

Basic Elements

There are 16 elements considered essential for plant growth. The most essential are carbon (C), hydrogen (H), and oxygen (O). They make up the bulk of the plant's weight and are derived from air(in the form of carbon dioxide) and water. The remaining nutrients are found in the soil or must be added in the form of fertilizer.

    Nutrient elements required in large amounts are called macronutrients, the ones most associated with lawn care are nitrogen (N), phosphorus (P) and potassium (K). The three numbers on a bag on fertilizer refer to these three nutrients.

  • Nitrogen (N): is responsible for rich, lush growth and a healthy, dark, green color. These characteristics are important but must be balanced with the other nutrients to achieve optimum results. Too much nitrogen can result in a weakened plant and excessive top growth, resulting in an increased need to mow and a vulnerability to disease and stress.
  • Phosphorus (P): is vital in many plant functions on a cellular level including energy transfer and cell division. It is important in the formation of seeds, the development of roots and it also speeds plant maturity and helps the plant resist stresses. Phosphorus can accumulate in the soil with repeated applications and has restrictions in some areas.
  • Potassium (K): helps to promote strong stems and roots and is involved in maintaining a proper water balance within the plant. It aids in disease resistance and influences most of the reactions that take place within the plant cells. Its role in root development is crucial in the fall when preparing turf for winter.

    The other macronutrients are:

  • Sulfur (S): aids in root development and stimulates seed formation. It is sometimes included in fertilizer blends but normally adequately available in the environment.
  • Calcium (Ca): stimulates root development, is rarely deficient and needs to be in balance with magnesium and potassium to function correctly.
  • Magnesium (Mg): is an important part of chlorophyll and a deficiency will cause chlorosis. Aids in phosphorus uptake. Needs to be in balance with potassium and calcium.

    Micronutrients are elements that are required in very small amounts and rarely deficient in the soil but still may occasionally need to be added in the form of fertilizer if a soil test indicates a need. They are:

  • Boron (B)
  • Chlorine (Cl)
  • Copper (Cu)
  • Iron (Fe)
  • Manganese (Mn)
  • Molybdenum (Mo)
  • Zinc (Zn)

A proper balance of nutrients is crucial to turf health. Too much or too little of one element will affect many complex relationships and put stress on the plant. To find out more about the nutrition of your lawn, have your soil tested .

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