St. Augustine grass is responsive to nitrogen fertilizer in terms of color and growth rate. On sandy soils St. Augustine grass requires about 1 pound of nitrogen per 1,000 square feet per month during the growing season to maintain satisfactory color and density. At rates above 1 pound per 1,000 square feet, St. Augustine grass produces lush growth that is highly susceptible to insects and diseases. On heavier textured soils ° pound of nitrogen every month is adequate to maintain good color and growth. Thatch accumulation is also a problem when nitrogen fertilization exceeds the required rate.
Late fall fertilization of St. Augustine grass helps maintain color and density of the lawn into the winter and promotes early recovery of the grass in the spring. Thus, to extend the length of time a St. Augustine lawn is attractive, the lawn should receive about 1 pound of nitrogen every 30 to 60 days from early spring through late fall.
St. Augustine grass is sensitive to iron deficiency and readily develops chlorotic symptoms in alkaline or iron deficient soils. This deficiency can be corrected with foliar applications or iron sulfate or iron chelate. Soil applications of iron sources are less effective than foliar application in alkaline soils.
Potassium requirements for St. Augustine grass are about the same as for other grasses. About half as much potassium as nitrogen is required to maintain growth. Potassium has been shown to increase root growth, cold tolerance and drought tolerance in St. Augustine grass.