• Proper fertilization ensures healthy plant growth.John Block/Brand X Pictures/Getty Images
  
  Yard fertilizers contain essentially the same ingredients as agricultural fertilizers; their two main components are nitrogen and phosphorous. Fertilizers also contain potash to provide potassium to the lawn as well as trace nutrients and filler such as sand. Some yard fertilizers contain insecticides or herbicides in addition to these basic ingredients.
  
  

Nitrogen

• Soil contains nitrogen in the form of nitrate ion, ammonium ion or present in organic materials. Nitrogen proves most important in plant growth, but is also most likely to leach in to local groundwater supplies. Take care to use no more than the recommended amount in an area and use slow-release versions to avoid this effect. Signs of inadequate nitrogen content include yellowing, slow growth and stunted size.
  
  

Phosphorous

• Phosphorous is a naturally occurring chemical found in rocks that slowly release the substance over time as the rocks weather. Although it can contaminate the environment when applied excessively, when used in proper amounts, phosphorous does not pose a problem because it binds quickly to soil and does not leach easily. Dry, cold soils and those with a high or low pH level are most likely to need additional phosphorous application for best plant growth. Signs of low phosphorous levels include dark green to purple colored foliage, slow growth and dying off of older leaves.
  
  

Potassium

• Adequate potassium levels in the soil ensures hardiness during cold times, disease resistance and plant durability. Potassium sometimes leaches, especially in sandy soil, but proves vital to healthy plant growth, being one of the three macronutrients needed by all plant life. Plants with low potassium levels show symptoms such as scorching on leaf margins, weakened stems and poor fruit development.
  
  

Trace Nutrients

• Yard fertilizer often contains other trace elements needed for plant growth. Some of these trace nutrients are added by use of a particular filler, such as lime. Homeowners need not concern themselves with the trace mineral content of yard fertilizer, as most soil already contains adequate amounts. The exception is the homeowners using only synthetic fertilizer which carries no trace minerals; they may need to add these through the use of organic material such as compost or mulch.
  
  

Filler

• Filler such as sand or finely ground limestone or corn cobs adds bulk to fertilizer and allows for even application. Some filler makes fertilizing and application easier, protecting a lawn from the effects of excess fertilization, such as burning.
  
  

Pesticides

• Yard fertilizers include insecticides or herbicides to eradicate pest problems in the yard. These prove useful to homeowners trying to solve such a problem while simultaneously feeding a lawn. They should not, however, be used without just cause, as this adds chemicals to the environment unnecessarily and affects local plants and animals and increases the problem of groundwater contamination.