Fertilizing St Augustine grass in Polk County
To produce an attractive lawn, St Augustine grass requires regular applications of fertilizers. Knowing the proper amount of fertilizer to apply requires knowledge of the soil’s fertility and knowledge of fertilizers. To learn about the soil’s fertility it is recommended that a soil sample be collected and the sample sent to a laboratory for analysis. A soil sample kit with instructions and mailing materials can be obtained by calling the Polk County Extension Office at (863) 519-8677 or sending an e-mail to gammatwo@ufl.edu. A copy of the soil test report will be returned to you with recommendations on the amount of fertilizer to apply and when. A copy will also be sent to the Extension office so you can call if you have questions.
St Augustin grass requires nitrogen (N), phosphorus (P2O5), and potassium (K2O) in the greatest amount. Calcium (Ca), magnesium (Mg), and sulfur (S) are required in smaller amounts. Micronutrients - iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), chlorine (Cl), molybdenum (Mo), and boron (B) are required in very small amounts but are as essential as N, P2O5 & K2O. Central Florida soils are naturally high in phosphorus. Applying more phosphorus than your grass needs will likely result in pollution of lakes and streams. Look for a fertilizer with 0, 1, or 2% phosphorus unless a soil test indicates your lawn needs more.
Fertilizers available at your discount store or garden center are sold on the basis of the plant nutrients they contain. Printed on the bag are three numbers such as 8-8-8 or 16-4-8. The numbers show the % of nitrogen (N), phosphorus (P2O5), potassium (K2O) in that order. Stated another way an 8-8-8 fertilizer has 8 lbs of N, 8 lbs of (P2O5) and 8 lbs of (K2O) in each 100 lbs of fertilizer. In addition, many fertilizers contain minor and micronutrients. Florida law requires that each bag have a tag attached or printed on the bag which details the plant nutrients in the bag. Examine the tag to see what you’re buying.
Of the three major nutrients, nitrogen is needed in the greatest amount by St Augustinegrass. Nitrogen fertilizers may be water-soluble and/or slow-release. Because water-soluble nitrogen may be easily leached (washed) from the soil by rain and irrigation, only small applications of water-soluble nitrogen should be used at one time. Common water-soluble forms of nitrogen include: ammonium nitrate, urea, ammonium sulfate or sodium nitrate. Synthetic slow-release forms of nitrogen include: sulfur coated urea, ureaform/nitroform, Nutralene and Polyon. A few of the natural organic slow release materials are: sewage sludge (Milorganite), cow manure and poultry manure. The fertilizer tag will list the percent of nitrogen that is slow release or insoluble.
Sometimes during the summer St Augustine grass will turn yellow indicating a lack of nitrogen. However, fertilizing with nitrogen in the summer is not desirable because nitrogen often encourages disease and insect problems. Applying iron (Fe) to St Augustine grass will often result in the desirable dark green color without stimulating excessive grass growth from a nitrogen application. Iron sulfate (2 ounces per 3 to 5 gallons of water per 1,000 square ft.) or a chelated iron source may be used to provide this greening effect. The greening from a supplemental iron application is temporary (approximately 2 to 4 weeks), as a result repeated applications are needed for summer long color.
When fertilizing St Augustine grass, apply a slow-release form of nitrogen or a combination of water-soluble and slow-release. Apply no more than ½ lb water-soluble or 1 lb slow-release nitrogen per 1,000 square ft. per application. If you have had your soil tested apply the amount of phosphorus (P2O5) and potassium (K2O) recommended by the soil test. In the absence of a soil test apply a complete fertilizer with an analysis such as 16-4-8 or 12-2-12 with minor elements.
To determine the amount of fertilizer to apply per 1,000 sq ft., divide the percent of nitrogen in the fertilizer into 100. If you’re using 16-4-8, divide 100 by 16 (100÷16=6.25 lbs). If all of the nitrogen is water soluble then apply only half pound of nitrogen or 3.12 lbs. per 1,000 square feet. If the nitrogen in the fertilizer is ½ water soluble and ½ slow release then you may apply one lb. of nitrogen since only ½ is water soluble.
There are three fertilizer programs for St Augustine grass in Polk County. The basic or low maintenance program will result in a minimum quality turf grass. The second level is a moderate program which will result in an intermediate-quality turf grass. The third level is a high maintenance program which should produce a high quality turf grass with good color and growth characteristics.
Only three fertilizer applications are needed for the basic program. Two applications of a complete fertilizer such as 16-4-8 should be applied, one in March and the second in September. The third application is an iron (Fe) application in June. The moderate program calls for five fertilizer applications: complete fertilizer in March and in October, an application of slow release nitrogen in May and August plus an iron application in July. The high maintenance program calls for six applications: complete fertilizer applications in February and October, a ½ lb. per 1,000 sq ft of water soluble nitrogen in April plus slow-release nitrogen applications in May and August with an application of iron in July.
St Augustine grass is the most popular turf grass for home lawns in Polk County. It remains a major challenge to maintain attractive turf areas while protecting our water bodies from pollution from excess or improperly applied fertilizer materials.
References:
Sartain, J.B. 2007. General Recommendations for Fertilization of Turfgrasses on Florida Soils. Florida Cooperative Extension Service, IFAS, Univ. of Fla. Pub # SL21. edis.ifas.ufl.edu/LH014
Trenholm, L.E., J.L. Cisar, and J. Bryan Unruh. 2006. St Augustinegrass for Florida Lawns. Florida Cooperative Extension Service, IFAS, Univ. of Fla. Pub # ENH5. edis.ifas.ufl.edu/LH010