St. Augustine grass (Stenotaphrum secundatum) is a common warm-season turfgrass prized across the southern United States for its dense, blue-green appearance and coarse texture. It forms a thick, carpet-like surface that thrives in the heat and humidity of its primary habitat along the Gulf Coast and into the transition zones. As a tropical species, it is inherently intolerant of prolonged cold, making winter preparation a necessary annual practice for homeowners. Understanding how this grass responds to dropping temperatures is the first step in ensuring its survival through the colder months.
The Critical Temperature Threshold
St. Augustine grass manages cold stress through a mechanism known as dormancy, a temporary shutdown of growth to conserve energy. This process typically begins when air temperatures drop consistently below 55°F, causing the leaf blades to turn a brown or tan color as the plant focuses its resources on the root system. This color change is a natural survival response and should not be mistaken for death, as the grass is simply resting until warmer weather returns.
The point of permanent damage, or physiological death, is reached when cold penetrates deeply enough to kill the rhizomes and stolons. While the grass can tolerate short-term air temperatures just below freezing, sustained temperatures that drop below 20°F can be lethal. The vulnerability of St. Augustine grass is heightened because its runners grow above the soil line, offering them less insulation compared to grasses with deep-seated rhizomes.
Soil temperature plays a significant role in survival, as the soil acts as a buffer against extreme air temperature fluctuations. If ground temperatures remain above the critical 10°F mark, the subterranean root system and the protected parts of the stolons have a higher chance of surviving. Harsh, prolonged freezes that penetrate the soil deep enough to kill the root crown are the primary cause of widespread turf loss during winter.
Identifying Cold-Tolerant Cultivars
Not all St. Augustine varieties possess the same degree of cold tolerance, which is an important consideration for planting in the northern limits of the grass’s adapted zone. Certain cultivars have been specifically developed or identified for their superior ability to withstand lower temperatures. The variety ‘Raleigh’ is widely recognized for its cold hardiness, having been bred to succeed in the transition zones of the upper South.
‘Palmetto’ is another popular choice, known for its good cold tolerance, often retaining its color longer into the winter than other varieties. This cultivar is reported to survive temperatures near 0°F, demonstrating notable resilience for a warm-season grass. These hardier varieties contrast sharply with cold-sensitive types, such as ‘Floratam,’ which is better suited for the deepest South and is much more susceptible to freeze injury.
Selecting a cultivar with proven cold tolerance is the most effective proactive measure a homeowner can take against winter damage. For instance, the ‘Sola’ cultivar, developed by NC State, is another example of a variety engineered to perform well in colder weather.
Preparing the Lawn for Winter
Preparing St. Augustine grass for winter involves cultural practices designed to promote cold hardiness and reduce the risk of vulnerable new growth. One of the most effective steps is to adjust the mowing height in the late summer or early fall as nighttime temperatures begin to drop below 70°F. Raising the cutting height to between 3 and 4 inches provides extra leaf blade insulation, which helps protect the delicate stolons and crowns from frost penetration.
The late-season fertilization strategy is important, requiring a shift away from nitrogen-heavy products. Homeowners should cease applying nitrogen fertilizer in mid to late September to prevent the flush of tender new growth that is highly susceptible to cold injury. Instead, an application of potassium (potash) in the fall can strengthen the turf’s cell walls and enhance its resilience to cold stress.
Irrigation practices must also be scaled back as the grass enters its semi-dormant state. The lawn still requires some moisture to prevent desiccation during dry, windy winter periods. Applying approximately 3/4 inch of water every 10 to 14 days during extended dry spells is usually sufficient to keep the root system viable without encouraging fungal issues.
Assessing and Recovering from Winter Damage
Once spring arrives, a homeowner’s immediate concern is distinguishing between dormant grass and grass that has suffered freeze injury. Dormant St. Augustine grass will be uniformly brown but will resist being pulled up easily, indicating that the root system is intact and alive. In contrast, patches of dead grass will appear straw-like, pull up easily with little resistance, and may have brittle, dark-colored roots.
Recovery efforts should begin only after the threat of a late-season frost has completely passed. Avoid raking the dead grass, as the brown material acts as a protective layer, insulating any live runners underneath. Raking too early can expose these vulnerable runners to further cold damage or desiccation.
When the turf shows clear signs of green-up, typically in mid-to-late spring, a light fertilizer application can be made. It should initially focus on root stimulation rather than top growth. Applying a fertilizer with a higher phosphorus content encourages the re-establishment of a strong root system before pushing aggressive leaf blade growth. Areas with extensive, permanent damage that fail to green up may require the installation of new sod to restore a uniform lawn.