St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze] is widely used for Florida lawn grass. At present phosphorus (P) fertilization of Florida lawn grasses is based on soil tests which were designed for agronomic crops in a production culture. Little information exits relative to the exact P requirement of St. Augustinegrass. The objective of this research was to determine the critical P requirement of St. Augustinegrass. Data collected in soil studies included visual quality rating, top growth rate, tissue P concentration, soil test P concentrations, and leachate volume and soluble reactive P concentration. From the soil studies, the minimum P application rate to achieve the maximum growth rate was 0.31 g P2O5 m-2 4-wk-1; the critical minimum tissue P concentration were determined to be 1.8 g kg-1. Mehlich-1 P, Fe Oxide Strip P, and WEP were highly correlated to each other and they were also highly correlated to tissue P concentration and top growth rate. Mehlich-1 was the best soil P extractant for St. Augustinegrass. The critical soil Mehlich-1 P levels were in the range from 5 to 9 mg kg-1 depending on soil properties. Most of the applied concentrated superphosphate did not leach below the top 2 cm of soil. Based upon these research findings, 0.31 g P2O5 m-2 4-wk-1 is recommended for St. Augustinegrass only if the soil Melich-1 P concentration is below 10 mg kg-1. Otherwise, no P application would be recommended.