There are many types of fertilizer available for use on lawns. Complete fertilizers contain nitrogen (N), phosphorous (P) and potassium (K) and are widely used for lawn fertilization . Every fertilizer material, must carry a label stating a guaranteed analysis of the material in it.
The Guaranteed analysis or fertilizer grade is a listing of nutrients contained in the bag, by weight. The first number is the percentage of N (nitrogen), the second number percentage of P (phosphate), and the third number percentage of K (potash).
Occasionally, a fourth number may appear prominently on the label. In turf fertilizers, this fourth number usually represents either iron (Fe) or sulfur (S), two supplemental nutrients that may be used under certain conditions.
In addition to listing percentage of nitrogen (N), phosphorous (P) and potassium (K) by weight, the label of a turf fertilizer also describes how much of the total N is water insoluble nitrogen (WIN). WIN is nitrogen which is slowly released for use by the turf grass over a long period of time (several weeks, months) as opposed to quickly available water soluble nitrogen (WSN). For lawn maintenance, a fertilizer containing both WSN and WIN is desirable. WSN is quickly available to the turf and thus provides improved color and growth very soon after application. However, it is more likely to cause foliar burn at higher rates. or during periods of hot, dry weather. At normal rates of 1 lb. of N/1000 sq. ft., the response from WSN will last approximately 4-6 weeks depending upon weather conditions. If a longer period of response (and thus fewer applications) is desired, a fertilizer containing some of the N as WIN should be used.
WIN is slowly released by one of several mechanisms and, therefore, is less likely to cause foliar burn; it provides a longer lasting response than quickly available WSN. It is also more expensive per pound of N applied, especially if the WIN is derived from natural organic sources such as sewage sludge, plant extracts, and proteins.
Most fertilizer bags will give you a chart listing different kinds of spreaders and the appropriate settings to achieve proper results when applying the product. Remember that it is better to be a little less than a little more to prevent lawn damage.
If you are in doubt about what type of fertilizer to use you should ask one of the people at your lawn and garden center. But it is really advised that before you start your fertilizer program you should get a soil test done to be sure that you will be supplying what the soil is lacking for optimum top and root growth.