St. Augustine grass (Stenotaphrum secundatum) is a warm-season turf known for its broad, bluish-green blades and dense, carpet-like growth, making it a popular choice in tropical and subtropical climates. This grass spreads aggressively by above-ground runners, called stolons, which form a thick mat that crowds out weeds. Patchiness is a common frustration for homeowners, often signaling that the grass’s needs for sun, water, or nutrients are not being met, or that an external threat has taken hold. Successfully repairing a patchy St. Augustine lawn requires diagnosing the root cause before attempting any physical repair, ensuring the new grass has a healthy environment in which to thrive.
Identifying the Root Cause of Patchiness
Diagnosing the precise reason for dead or thinning patches is the most important step, as replanting without fixing the underlying issue will lead to recurrence. The pattern and location of the damage offer the first clues, helping to distinguish between pests, disease, and environmental stress.
Pest damage often comes from the Southern chinch bug, a small, sucking insect that injects a toxin into the grass blades. Damage appears as irregular, expanding patches of dead, straw-colored turf, typically found in the hottest, sunniest areas. These patches often have a border of yellowing grass. The insects—small, black-bodied adults with white wings, or reddish nymphs—can be confirmed using a float test.
Fungal disease issues present with visual signatures that distinguish them from insect damage. Brown Patch, caused by Rhizoctonia solani, is common during periods of high moisture and moderate temperatures. This disease creates circular patches of affected grass, one to five feet in diameter, often causing leaf blades to easily slip away from the runner. Gray Leaf Spot presents as small, diamond-shaped lesions with gray centers and purple or brown margins, leading to a scorched appearance in severe cases.
Environmental or cultural factors frequently cause decline, weakening the turf and making it susceptible to pests or disease. St. Augustine grass requires significant sunlight; excessive shade causes thinning and fungal problems. Compacted soil prevents roots from accessing air, water, and nutrients, leading to patchy growth. Compaction is likely if a screwdriver stops hard at two inches when pushed into the ground. Poor drainage, over-fertilization, or chronic under-watering also stress the grass, causing decline.
Preparing the Soil and Patch Area
Once the root cause is addressed, physical preparation of the patch area must begin to create a healthy bed for the new grass. The first step is removing all dead, straw-colored plant material, which may involve vigorous raking or light dethatching. Decaying material can harbor disease spores and prevent new grass runners from making contact with the soil.
If soil compaction was identified, the area should be aerated using a core aerator to perforate the soil, creating small holes two to three inches deep. This allows air, water, and nutrients to penetrate the root zone, improving soil structure for new growth. After aeration, the soil should be loosened with a cultivator or rake to a depth of several inches, ensuring new roots can easily penetrate and establish.
The next step is to amend the soil, ideally based on a recent soil test to check pH and nutrient levels. St. Augustine grass prefers a slightly acidic to neutral pH (6.0 to 7.5). Adding a layer of organic matter, such as composted manure, and raking it into the loosened soil improves drainage and fertility. The area should be leveled and lightly firmed before planting, ensuring the final grade is slightly below adjacent sidewalks or driveways.
Specific Methods for Replanting St. Augustine
St. Augustine grass is a sterile turf that cannot be reliably grown from seed, making vegetative propagation the only option for repair. The choice of method—sod, plugs, or runners—depends on the size of the patch, the urgency of the repair, and the available budget.
Laying sod is the fastest method for repairing large, dead areas, providing an immediate, uniform cover. Sod pieces should be laid in a staggered, brick-like pattern, ensuring the seams are tightly butted against one another to prevent drying. After laying, the sod must be firmly tamped or rolled to ensure complete contact between the sod’s root system and the prepared soil bed.
Plugging is a cost-effective alternative for medium-sized patches or thin areas, involving planting small pieces of established sod. Plugs are typically spaced 12 inches apart in a checkerboard pattern, allowing the aggressive stolons to spread and fill in the gaps over time. When planting, the top of the plug should be level with the surrounding soil, and the hole should be deep enough to accommodate the root ball without burying the grass blades.
Using runners or sprigs is the slowest but least expensive method, often used for small, scattered patches. Runners are sections of above-ground stolons that can be laid in shallow trenches or pressed into loose soil, with the cut ends covered. The exposed leaves should remain above the soil line, and the area must be kept consistently moist until the runners root and begin to spread.
Post-Repair Establishment Care
The initial care immediately following planting is crucial for encouraging deep root growth and ensuring the new grass establishes itself permanently. For the first one to two weeks, the newly planted sod, plugs, or runners require frequent, light watering to keep the surface and underlying soil consistently moist. This prevents the delicate new root systems from drying out, which may require watering multiple times per day.
After the first two weeks, the watering schedule should transition to less frequent but deeper applications to encourage the roots to grow downward into the soil. The goal is to water enough to moisten the soil to a depth of three to four inches, which promotes a more drought-tolerant turf over time. Overwatering beyond this initial establishment period can lead to disease, so it is important to check for signs of new white root growth before reducing frequency.
A starter fertilizer, low in nitrogen and high in phosphorus, should be applied two to three weeks after planting to stimulate root development. Phosphorus is important for establishing a strong root system, rather than rapid leaf growth. New sod and plugs should be protected from heavy foot traffic for the first three to four weeks to avoid dislodging new growth. The first mowing should be delayed until the new grass is firmly rooted and has reached a height of about three inches.