I have had a couple of fertilizer questions this week so I thought I would share some information.  Calculating the correct fertilizer rate is important for most lawns.  The old saying, “If a little is good more is better” may not apply in this situation.

Over fertilization of centipede lawns can lead to excessive growth with shallow root systems that will eventually crash.  A modest fertilization program is important to maintaining healthy, attractive turf. It should include applying the correct type and amount of fertilizer at the right time. Proper fertilization is generally the most cost-effective practice to have a nice lawn. However, fertilization must be combined with proper mowing, watering and pest management for best results.

A fertilizer grade or analysis is the percentages of nitrogen (N), phosphorus (P2O5) and potassium (K2O) in the material. A 12-4-8 grade fertilizer contains 12 percent N, 4 percent P2O5 and 8 percent K2O per 100 lbs. of fertilizer.  Georgia law requires fertilizer producers to display the guaranteed analysis (grade) on the fertilizer container.  A 50-pound bag of 12-4-8 fertilizer will contain 6 lbs. of N, 2 lbs. of P and 4 lbs. of K.

Turfgrass fertilizer recommendations are given in pounds of actual nutrient like nitrogen (N), phosphorus (P2O5) and potassium (K2O) per 1000 square feet of area. An example of a common grade of fertilizer and the amount needed to meet the recommendations is also provided.  Many different grades of fertilizer are available that can be used to meet these soil test recommendations. Remember: The soil test recommendations are guidelines, not absolute quantities. If you cannot find a fertilizer grade that matches the recommended ratio, use the fertilizer grade that is closest to it.

The application rates can be changed for larger areas like an acre very easily.  If the recommendation says it will take 8.3 pounds of 12-4-8 to supply one pound of nitrogen to a 1000 square-foot area, you will need 362 pounds of 12-4-8 per acre to accomplish this because there are 43,560 square feet in an acre.

Since most of our lawns are centipede I will focus on it in this article, if you have questions about fertilizing other turf species please call or come by the office.  Centipede has a natural light green color and is suited to acid soils (pH 5.0 to 6.0) but grows best at a higher pH. High rates of fertilizer, especially nitrogen, will produce a dark green color but will also lead to growth problems.  One to two lbs. of nitrogen per 1000 square feet per year is generally good for centipede, although it will grow well without any fertilizer. The 2 lb. rate may be preferable on sandy soils.  Apply nitrogen in split applications. Apply the first two to three weeks after spring green-up and the second in midsummer (July – August).

Determine phosphorus and potassium needs by soil testing. If soil testing is not used, a general purpose fertilizer with a 3-1-2 nitrogen-phosphorus-potassium (N-P2O5-K2O) ratio such as 12-4-8 is good.  Apply 5 pounds of 12-4-8 per 1000 square feet after spring green-up and again in midsummer.  Another possible choice of fertilizer is 4 pounds of 16-4-8 per 1000 square feet after spring green-up and in midsummer.  Apply the fertilizer evenly over the area when the grass leaves are dry. Remember, avoid excessive fertilization and avoid early spring applications.