St. Augustine, a warm-season turfgrass common in the Southern United States, turns brown when temperatures drop in winter. This color change is not a sign of death, but rather a normal, protective process called dormancy. As a survival mechanism, the grass redirects energy and resources away from the visible green blades and into the root system. This temporary shutdown allows the plant to endure cold periods with minimal damage, ensuring it returns to vibrant growth when warmer weather returns.
St. Augustine Grass and the Dormancy Cycle
Dormancy is a biological response to unfavorable environmental conditions where growth slows significantly or stops entirely. For St. Augustine grass, this state is primarily triggered by consistently cool temperatures rather than a single frost event. The grass begins to slow its growth once air temperatures drop below approximately 65°F and enters full dormancy when soil temperatures fall below 55°F.
Once the trigger temperature is reached, the plant stops producing chlorophyll, the pigment responsible for its green color. The leaf blades turn a straw-colored tan or brown as the plant conserves energy and nutrients in its roots and above-ground runners, or stolons. This is essentially the grass “sleeping” to survive the cold, which is why the roots remain alive and firmly anchored in the soil.
Essential Winter Care Practices
Even while dormant, St. Augustine grass requires minimal, targeted care to prevent desiccation and damage. Proper winter watering is necessary because the root system can dry out in the absence of regular rainfall, a condition known as winter desiccation. During the cooler months, watering should be infrequent, perhaps every 10 to 14 days, but deep enough to keep the roots viable. Aim to provide about three-quarters of an inch of water per session to moisten the soil without causing saturation.
Mowing frequency should drop dramatically since the grass is not actively growing, but it is important to maintain a slightly higher cut of around 3.5 to 4 inches. This extra blade height helps insulate the stolons and crowns, providing protection from cold snaps. Applying nitrogen fertilizer is strongly discouraged during dormancy because it can encourage new, tender growth highly susceptible to cold injury and freeze damage. Instead, a late-fall application of a fertilizer higher in potassium can help strengthen the root system and improve cold tolerance before winter.
Telling the Difference Between Dormancy and Damage
It can be difficult to differentiate between healthy dormancy and grass that is damaged or dead. Dormancy typically presents as a uniform, straw-brown color across the entire lawn, with the grass still feeling somewhat pliable and resisting being pulled from the soil. You can perform a “tug test” by gently pulling on a handful of grass; dormant grass will resist, confirming the roots are intact.
In contrast, damage often appears in irregular or circular patches of brown, indicating a problem rather than a systemic shutdown. One common issue is Brown Patch disease, a fungal infection that thrives in cool, moist conditions during the fall and winter. This disease forms roughly circular patches that can range from a few inches to several feet across, sometimes displaying a distinct yellow or dark ring around the perimeter. Damage from cold injury or disease will result in grass that is easily pulled out or has rotting leaf sheaths near the soil surface.
Preparing for Spring Recovery
The transition out of dormancy, known as spring green-up, is a gradual process for St. Augustine grass. Active growth resumes when soil temperatures consistently reach the mid-60s, which usually occurs in late spring. Homeowners should exercise patience, as St. Augustine is known to be slow to fully green up, especially after a harsh winter.
Initial spring activities should involve light raking to remove excessive dead material, which helps sunlight reach the stolons and speed up soil warming. However, avoid aggressive raking or scalping the lawn, as this can damage the delicate runners that are just beginning to grow. The first application of a nitrogen-based fertilizer should be delayed until the grass is fully green and actively growing, ensuring the plant can effectively use the nutrients. Once the threat of the last frost has passed and new growth is visible, gradually increase watering frequency to support the renewed metabolic activity.