St. Augustine grass is a popular warm-season turfgrass, especially in the southern United States, known for creating lush, dense lawns. It features broad, flat blades that can range from bluish-green to dark green, forming a thick, carpet-like mat that effectively suppresses weeds. This grass spreads through above-ground runners called stolons, allowing it to establish quickly and provide robust coverage. While it thrives in the heat and humidity of its preferred climates, a common concern for homeowners is its susceptibility to cold temperatures.
Understanding St. Augustine Grass Cold Tolerance
St. Augustine grass is a warm-season variety, meaning it performs best in temperatures above 65°F (18°C) and enters a state of dormancy as conditions cool. Dormancy is a natural defense where growth slows or ceases to conserve energy, often turning the grass brown or tan. The grass typically begins to show stress when temperatures consistently drop below 50°F (10°C).
Significant damage or even death can occur if temperatures remain prolonged below critical thresholds. It is particularly susceptible to winter injury in regions with extended cold. While it can withstand short dips, temperatures consistently below 20-25°F (-6 to -4°C) can lead to considerable harm. Soil temperatures around 10°F (-12°C) can cause shock and damage.
Recognizing Cold Damage
When St. Augustine grass experiences cold stress or frost, visual changes become apparent. The leaf blades may begin to brown or take on a purplish hue. This discoloration can progress to a dull, straw-like appearance, and the grass may seem wilted. These symptoms often emerge after a cold snap.
It is important to differentiate between temporary dormancy and permanent tissue damage. While dormant grass turns brown or tan as a survival mechanism, it retains the ability to green up once warmer weather returns. In contrast, permanently damaged grass will not recover, showing dead tissue that feels brittle. Poorly drained or exposed areas may exhibit more severe browning and matting.
Factors Affecting Cold Hardiness
Several elements influence St. Augustine grass’s cold endurance. The specific cultivar plays a significant role, as some varieties exhibit greater cold tolerance than others. For instance, ‘Raleigh,’ ‘Palmetto,’ and ‘Mercedes’ are generally more cold-hardy, while ‘Floratam’ is notably more susceptible to cold. Overall turf health and vigor contribute to its resilience, as well-maintained lawns better withstand environmental stresses.
Proper nutrition, with adequate potassium, improves cold hardiness. Soil compaction can hinder root development and drainage, making the grass more vulnerable to cold injury. Newly laid sod is typically more susceptible to cold damage than established lawns, as it has not yet developed a robust root system. Microclimates within a lawn, such as under tree cover or on slopes, can offer protection from direct cold and wind.
Protecting St. Augustine Grass from Winter
Proactive measures are key to minimizing cold damage in St. Augustine grass during colder months. In fall, a balanced, slow-release fertilizer with higher phosphorus and potassium can promote root growth and improve cold tolerance. Avoid nitrogen late in the season to prevent vulnerable new growth. Watering adequately before a freeze is important, as moist soil provides better insulation for the roots and prevents dehydration.
Adjusting mowing height is beneficial; raising the blade to 3.5 to 4 inches for cooler months helps insulate the grass and protect the root system. For smaller, vulnerable areas or newly planted sod, use protective covers like breathable fabrics or frost cloth to shield delicate grass by trapping warmth. Clearing debris and ensuring good drainage helps prevent water from pooling and freezing on the turf.