St. Augustine grass (Stenotaphrum secundatum [Walter] Kuntze) is a warm-season grass that grows in U.S. Department of Agriculture plant hardiness zones 8 through 10. It has high tolerance for heat, shade and drought along with a low tolerance for cold weather. The grass blades are 4 to 10 millimeters wide and folded down the center, with leaves opposite each other at the leaf nodes. Maintain St. Augustine grass weed-free by obeying the proper irrigation and fertilization schedule for your lawn. The amounts of each will be different based on the soil type and the number of rainfall you have.
Look carefully at the grass stems. St. Augustine grass stems have rolled leaves in the stem, while invasive sedges like green kyllinga (Kyllinga brevifolia) and nutsedge (Cyperus spp.) have triangular-shaped stems.
Examine the leaves. Broadleaf weeds are easily differentiated from grass leaves. White clover (Trifolium repens) and creeping woodsorrel (Oxalis corniculata) have rounded clusters of leaves and grow in patches near the ground. Plantains (Plantago major) have elongated, oval-shaped leaves which grow from a base. Spurge (Euphorbia maculata) has multiple tiny leaves on long, spreading stems. Dandelions (Taraxacum officinale) have sharp leaves with pointed edges and fuzz. English daisies (Bellis perennis) have succulent-like leaves. Grass weeds can be more difficult to distinguish. Goosegrass (Eleusine indica) is dark green with a silvery leaf base. Like groosegrass, crabgrass (Digitaria spp.) Grows in tufts but is also a lighter green without a silvery shade.
Use the dirt condition to help identify the most likely weeds. Annual and perennial grasses grow in St. Augustine grass that’s over-watered, grown in compacted dirt or mowed too brief. Annual and perennial broadleaves invade grass that’s nitrogen-deficient or contains thin patches in the lawn. Sedges like areas with poor drainage and frequently show up in hot, sunny weather.