St. Augustine grass is a popular warm-season turf known for creating a dense, carpet-like lawn across many southern regions. While homeowners see the vibrant green blades, the true measure of the lawn’s health lies beneath the surface in its root system. A robust root structure is the foundation that allows the grass to survive periods of heat, drought, and disease pressure. Encouraging deep root growth is the most important factor in maintaining a thriving St. Augustine lawn, as the roots dictate the grass’s ability to absorb water and nutrients.
Understanding Root Structure and Depth
St. Augustine grass spreads primarily through above-ground runners called stolons, which creep horizontally across the soil surface. These stolons produce new shoots and a dense network of fine, fibrous roots that anchor the plant and absorb essential resources. Due to this fibrous structure, St. Augustine naturally tends to have a shallower root system compared to other turf varieties.
For a healthy, resilient lawn, the roots should penetrate the soil to an average depth of at least six inches. In optimal conditions, roots can extend to 12 inches or more, though the highest density remains in the top few inches of the soil profile. Shallow roots make the grass highly vulnerable to heat stress and rapid dehydration, requiring constant, light watering. Encouraging growth to the optimal depth provides access to a larger volume of soil moisture, resulting in a more drought-tolerant turf.
Essential Care Practices for Deep Root Growth
The most effective way to strengthen a St. Augustine lawn is through specific cultural practices that force the root system to grow downward in search of moisture. This process, known as deep, infrequent watering, is fundamental for developing turf resilience. Instead of applying small amounts of water daily, soak the soil thoroughly to a depth of six to eight inches, delivering about one inch of water per week. Allowing the soil surface to dry out between these deep watering cycles encourages the roots to chase the receding moisture deeper into the ground.
Maintaining a correct mowing height also directly impacts the depth of the root system. Turfgrass research consistently shows a direct correlation between the height of the leaf blade and the depth of the roots. Mowing St. Augustine grass between 3 and 4 inches is recommended, as this taller canopy provides more surface area for photosynthesis and shades the soil, keeping it cooler. Cutting the grass too short stresses the plant, restricts the root mass, and makes the lawn weaker and more susceptible to environmental stress.
The approach to fertilization must focus on long-term root health rather than rapid top growth. Excessive application of quick-release nitrogen stimulates lush blade growth at the expense of root development. Instead, use a balanced fertilizer schedule that includes slow-release nitrogen sources to sustain steady growth. Potassium is a nutrient that strengthens the grass plant, supporting a more robust and disease-resistant root structure.
Identifying and Treating Common Root Issues
Several common problems directly target the St. Augustine root system. One of the most significant fungal diseases is Take-All Root Rot (TARR), caused by the fungus Gaeumannomyces graminis. Symptoms include yellowing and thinning of the grass blades, often appearing in irregular patches during the spring and early summer. A defining symptom is the ease with which the affected grass can be pulled up because the roots have rotted away.
Treatment for TARR involves improving soil conditions, as the fungus thrives in poorly drained, compacted soil, and high pH levels. Applying a layer of sphagnum peat moss helps by lowering the soil’s pH to a more acidic level, which inhibits the fungus. Fungicides containing active ingredients like azoxystrobin can also be used as part of a treatment plan.
Another threat comes from pests that feed directly on the roots, such as white grubs. These C-shaped larvae chew through the roots, causing the grass to detach from the soil in affected areas. If you can easily lift sections of turf like a piece of carpet, grubs may be the cause, requiring inspection of the underlying soil.
Soil compaction is also a major mechanical problem, physically restricting root growth and preventing water and air from reaching deeper soil layers. Core aeration, which removes small plugs of soil, is the primary method to alleviate compaction and allow the roots to penetrate more deeply.