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 basically designed for agronomic crops in a production culture. Little information exits relative to the exact P requirement of St. Augustinegrass. The objective of this study was to determine the critical P requirement of St. Augustinegrass using solution culture techniques. Established pots of ‘Floratam' were subject to the P treatments in solution culture at a range between 0 and 775 mg m^-3 P for 148 d. Measurements included tissue and root growth rates, tissue and root P levels and visual rating of turfgrass quality. Phosphorus treatments increased tissue and root P levels with each successively higher P level. The best turf quality was achieved by the highest P treatment. Turfgrass receiving 31 mg m^-3 P gained the highest root growth rate among the treatments. The tissue growth rate was increased with P treatments in a quadratic manner to a maximum value. According to linear plateau regression analysis, the critical solution P concentration was 153 mg m^-3 and the critical tissue P level was 1.4 g kg^-1 on dry weight basis for the optimum growth. Given the critical tissue P level, it needs further research in soil to determine the minimum fertilization level of St. Augustinegrass to achieve the critical tissue P level.