Fertilizing the lawn is a great way to improve its quality and is one component of turfgrass maintenance required to have a thick, lush stand of turf. How much fertilizer to use depends on the turf species. Bermudagrass has a high nitrogen requirement, and if it doesn’t receive enough nitrogen, it can become thin and weedy. Centipedegrass has a low nitrogen requirement, and too much fertilizer will lead to turf decline and possibly disease.
Knowing when to apply fertilizer is just as important as using the proper amount. Warm-season grasses are just beginning to green up in South Carolina. It usually only takes a few days in the mid-seventies to see green blades popping up in warm-season lawns. The grass is coming out of winter dormancy, but fertilizing too early can be harmful.
Warm-season grasses, like centipedegrass, bermudagrass, St. Augustinegrass, and zoysiagrass actively grow and thrive when air temperatures are between 75 and 95 ºF. New shoots will begin to emerge once soil temperatures reach 65 ºF at a 4-inch depth. The energy for this new growth comes from carbohydrates that are stored in the crowns, rhizomes, and stolons of the grass. Warm-season turfgrass roots die back in late winter and also need to regrow during spring green-up.
Lawn fertilizers usually contain a higher percentage of nitrogen than other nutrients, and nitrogen favors the growth of new shoots. Warm-season grasses fertilized too early in spring can produce a lot of new shoots at the expense of root production. This can set your lawn up for dieback from late-season frosts and leave the grass at a disadvantage with a diminished root system. Warm-season grasses can usually satisfy their early-season nitrogen needs by absorbing it from their environment as they come out of dormancy and slowly green-up.
Root and shoot growth increase as temperatures continue to warm up, so most warm-season grasses are actively growing by early to mid-May. This is when your lawn needs a fair amount of nitrogen, and demand cannot usually be met by environmental sources alone. A good rule of thumb is to wait to fertilize your warm-season grass until nighttime temperatures are around 70 ºF. For more information, please see HGIC 1201, Fertilizing Lawns.