Cooperative Extension Service 
Institute of Food and Agricultural Sciences
Hendry County Extension P. O. Box 68 LaBelle, Florida 33975-0068 Phone (863) 674-4092

Hendry County Horticulture News

Fertilizer Familiarity Pays Off

Whatever the season or crop, familiarity with fertilizers pays off. Successful gardeners know that a good fertility program leads to healthier and more productive plants and is essential before top yields and performance of fruit, flowers, vegetables and ornamental favorites can be expected.  Gardeners are often confused by terminology as it applies to commercial fertilizers. Such terms as mixed fertilizer, balanced or unbalanced, complete or incomplete have little or no meaning to many gardeners.  In addition to this they are even more confused when it comes to numbers on the fertilizer bag, such as 8-8-8 or 10-6-4.  What is the meaning of this cryptic terminology and confounded figures?  This column will  try to explain to  what these terms and figures mean as they apply to fertilizer.

A fertilizer is a material which contains one (or sometimes two or three) of the major plant food nutrients - nitrogen, phosphorus, and potassium.  To further confuse matters, the fertilizer elements are often denoted by the letter abbreviations:  N  = nitrogen, P =  phosphorus, and K = potassium or potash.

When two or more fertilizer materials are mixed, the product is called a "mixed fertilizer." If the mixed fertilizer contains all three of the major plant nutrients (nitrogen, phosphorus, potassium) it is called a "complete fertilizer". When only one or two of the nutrients are present it is referred to as an "incomplete fertilizer."

A "balanced" fertilizer is one containing the three major nutrients in equal amounts. An 8-8-8 fertilizer is a "complete balanced" fertilizer since it contains all three major nutrient elements and all three are present in equal amounts.

A "complete unbalanced" fertilizer is one that contains all three major nutrients but each is not present in equal amounts. A 10-6-4 fertilizer is an example of a "complete unbalanced" fertilizer.

Now, to get down to the specifics of what the numbers on the bag mean. The term 8-8-8 is the analysis or grade designation of a commonly available complete and balanced fertilizer. The grade or analysis of a fertilizer gives the percentage by weight of each of the three fertilizer nutrients. The percentages are expressed in terms of total nitrogen, available phosphoric acid and water-soluble potash.   Thus, an 8-8-8 fertilizer contains 8 percent total nitrogen, 8 percent phosphoric acid and 8 percent water-soluble potash. The nutrients are always listed in this order on the label attached to the fertilizer.

A 100 pound bag of 8-8-8, therefore contains 8 pounds of nitrogen, 8 pounds of phosphoric acid and 8 pounds of potash, or a total of 24 pounds of plant nutrients. The remaining 76 pounds consist of a filler or a carrier of some kind. These fillers may or may not have some value as a source of plant nutrients. Some fertilizer manufacturers include micro nutrients in the filler. The amount of the  micro nutrients sulfur, iron, magnesium, manganese, zinc, copper, chlorine, molybdenum and boron that are required by plants is very minute and is considerably less often than the amount of nitrogen, phosphorus and potassium needed to keep plants in good condition.

Two questions may come to mind. These are: Should you use a complete balanced fertilizer or a complete unbalanced fertilizer? How much should you use?   In general, a complete balanced fertilizer should be used. Without a soil test or years of observation and experience you have no way of knowing which of the three major nutrient elements may or may not be needed. Therefore, a complete fertilizer is recommended to take care of any possible deficiency of the three major nutrient elements.

As to how much to use, without a soil test, definite recommendations as to amounts to apply can not be given. General recommendations as to type and amount of fertilizer to apply are available from various sources. In some instances, research on plant growth and performance at various fertilizer regimes has lead to the development of more specific recommendations.  For example, 16-4-8 - a complete unbalanced fertilizer is often recommended for turf.  However, without a soil test, you may actually be over fertilizing or under fertilizing to some degree.

It's important use the right amount of fertilizer, since "too much of a good thing" may harm your plants or the environment.  The best advice is to collect a soil sample for analysis to determine how much fertilizer you should add to your soil at the beginning of the gardening season. The results of the soil fertility analysis will also tell you how much fertilizer should be added to your particular crop as the season progress. For more information on fertilizers or  the procedure for collecting a sample, check with the Hendry County Extension Office.  Good luck and good gardening.

Gene McAvoy is the horticulture agent with the Hendry County Extension Service.  Direct your horticulture questions to PO Box 68, LaBelle, FL 33975,  e-mail - or phone 863-674-4092 or  863-983-1598.  You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle.   Office hours are from 8:00 - 5:00.

The Institute of Food and Agricultural Sciences is an Equal Employment Opportunity - Affirmative Action Employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap or national origin.

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