St. Augustine grass (Stenotaphrum secundatum) is a popular, coarse-textured, warm-season turf across the Southern United States. This aggressive, stoloniferous grass thrives in the region’s heat and humidity, creating a dense lawn when properly maintained. Establishing a robust St. Augustine lawn depends on consistent care practices that support its unique growth pattern. Understanding these foundational requirements promotes the health and density of this desirable turf.
Essential Foundational Maintenance (Mowing and Watering)
The proper mowing height for St. Augustine grass is between 3 and 4 inches. Cutting the grass too short stresses the plant, leading to thinning and weed invasion. Maintaining a taller blade height encourages deeper root growth, making the turf more resilient to heat and drought. Adhere to the “one-third rule,” removing no more than one-third of the leaf blade’s total height in any single mowing session.
To follow the one-third rule, you may need to increase mowing frequency, especially during the peak summer growing season. Using a mower with a sharp blade is equally important, as a dull edge tears the grass blades, leaving jagged cuts that turn brown and invite disease. Varying the mowing pattern each time helps prevent soil compaction and ensures the grass blades are cut cleanly and uniformly.
St. Augustine grass requires deep and infrequent watering to encourage a strong, extensive root system. The goal is to provide approximately 1 inch of water per week, though this may increase to 1.5 inches during periods of extreme heat or in sandy soils. This weekly amount should be delivered in one to three separate sessions, allowing the top layer of soil to dry out between waterings.
Avoid shallow, frequent watering because it promotes weak, surface-level roots. The best time to irrigate is in the early morning, ideally before 9 a.m., allowing the grass blades to dry completely before nightfall. Watering in the evening leaves moisture on the leaf surface for an extended period, encouraging fungal development.
Strategic Nutrient and Soil Management
St. Augustine grass is a heavy feeder requiring a consistent supply of nutrients, especially nitrogen, throughout its active growing season. A soil test every few years determines specific nutrient deficiencies and the current soil pH level. Without a soil test, use a complete fertilizer with a nitrogen-phosphorus-potassium (N-P-K) ratio of 3-1-2 or 4-1-2.
Apply fertilizer seasonally, beginning in late spring after the grass has fully greened up and the danger of late frost has passed. Subsequent applications are timed for mid-summer and early fall to sustain vigorous growth without encouraging disease-prone lushness. The annual total nitrogen rate should be 2 to 4 pounds of actual nitrogen per 1,000 square feet, depending on soil type and desired density.
One common issue in St. Augustine lawns, particularly those in alkaline soils, is iron deficiency, or chlorosis. This presents as a distinct yellowing of the grass blades while the veins remain a darker green color. In this scenario, applying more nitrogen fertilizer is not the solution and can actually worsen the problem by encouraging growth that further outstrips the available iron supply.
Treatment for chlorosis requires applying a supplemental iron source, such as a foliar spray of chelated iron or iron sulfate. The plant absorbs this directly through the leaves for a rapid green-up. For a more sustained effect, acidifying soil amendments like elemental sulfur can be incorporated to gradually lower the soil pH, improving the grass’s ability to naturally access iron.
When applying any granular fertilizer, using a broadcast spreader and following the product label directions is necessary to ensure an even application and prevent turf burn.
Diagnosing and Treating Specific Lawn Problems
Weed Control
St. Augustine grass is sensitive to many common herbicides, necessitating careful selection for weed control. Applying a pre-emergent herbicide in late winter or early spring is the most effective preventative measure, stopping weed seeds from sprouting. Products containing active ingredients like prodiamine or atrazine are safe for St. Augustine turf when used according to label instructions.
For existing weeds, post-emergent selective herbicides are required, but avoid products containing 2,4-D or Quinclorac, which damage St. Augustine grass. Safer alternatives for broadleaf weed control include active ingredients such as atrazine or Celsius. Always spot-treat specific weeds rather than broadcasting a chemical application across the entire lawn to minimize turf damage.
Pest Management
The most destructive insect pest is the chinch bug, a tiny black insect with white patches that causes damage resembling drought stress. Infestations begin in the hottest, sunniest areas of the lawn, often alongside sidewalks or driveways where heat is retained. Chinch bugs feed by sucking sap and injecting a toxin, leaving irregular, spreading patches of yellow-to-brown, dead turf that does not recover after watering.
To confirm an infestation, inspect the border between the dead and living grass for the small, fast-moving adults or their orange, nymph-stage young. If chinch bugs are confirmed, treatment involves applying a contact insecticide, such as one with bifenthrin, directly to the affected areas. Multiple applications may be required to break the reproductive cycle, so follow the insecticide’s instructions precisely.
Disease Management
Fungal issues are common in St. Augustine, with Brown Patch, caused by the fungus Rhizoctonia solani, being a frequent concern. This disease is favored by high humidity and moderate temperatures, becoming active in the cooler, wetter periods of spring and fall. Symptoms first appear as circular or semi-circular patches of brown or yellowing grass that can range from a few inches to several feet in diameter.
The fungus attacks the base of the leaf blade, causing the leaf sheath to rot. Managing Brown Patch involves applying a systemic fungicide, with options like propiconazole or azoxystrobin being effective, especially when applied preventatively. Cultural practices, such as avoiding excessive nitrogen fertilization during peak disease periods and ensuring early morning watering, help reduce the conditions that allow the fungus to thrive.