St. Augustine grass (Stenotaphrum secundatum) is a popular warm-season turf known for its coarse texture and deep green color, thriving in tropical and subtropical climates. While often prized for its dense, carpet-like appearance, its overall health and resilience depend entirely on the strength and depth of its root system. A robust network of roots allows the grass to effectively absorb water and nutrients, enabling it to withstand high summer heat, drought, and heavy foot traffic. Cultivating deep, healthy roots is the most effective long-term strategy for maintaining a dense, vibrant lawn that endures challenging environmental conditions.
Anatomy of the St. Augustine Root System
The root structure of St. Augustine grass is fibrous, consisting of a dense mat of fine, thread-like roots extending outward and downward from the base of the plant. These true roots are the primary structures responsible for the uptake of moisture and dissolved minerals from the soil. While most of this fibrous network resides in the top four to six inches of the soil profile, healthy, established roots can reach depths of 12 inches or more.
The grass also utilizes specialized above-ground stems called stolons. Stolons creep horizontally along the soil surface, producing new shoots and adventitious roots at their nodes, which allows the grass to spread laterally and form a dense turf. The deeper, true roots anchor the plant and sustain it during periods of environmental stress, unlike the stolons which facilitate spreading.
Optimizing Soil and Water for Root Health
Promoting deep root growth requires careful management of the soil environment and a precise watering strategy. The most significant factor influencing root depth is the frequency and duration of irrigation. Providing deep, infrequent watering, where the soil is saturated to a depth of at least six to eight inches, stimulates the roots to grow downward in search of moisture. This capitalizes on the principle where roots are signaled to grow in the direction of the water source.
Conversely, shallow, frequent watering keeps only the top few inches of soil moist, conditioning the roots to stay near the surface. Surface roots are highly susceptible to rapid drying and heat stress. Apply approximately one inch of water per session, ideally in the early morning to minimize evaporation and reduce the risk of fungal disease.
The physical and chemical properties of the soil also play a decisive role. St. Augustine grass thrives in well-drained soil with a slightly acidic to neutral pH range, ideally between 5.0 and 7.5. Poorly drained or compacted soil drastically limits root penetration and restricts the movement of oxygen, which is necessary for root growth.
Compaction is common in high-traffic areas and can be mitigated through annual core aeration. Aeration pulls small plugs of soil, creating channels that allow air, water, and nutrients to reach deeper soil layers. This directly stimulates the growth of stronger roots. If soil pH is outside the optimal range, soil testing can guide the use of amendments to ensure nutrients are readily available.
Identifying and Addressing Root Stressors
A number of biological and physical factors can inhibit or directly attack the St. Augustine root system, leading to visible turf decline.
Biological Stressors
Among the most damaging biological stressors are soil-borne fungal diseases. Take-All Root Rot (TARR) proliferates in overly wet or stressed conditions, attacking roots and stolons. This reduces the plant’s ability to transport water and nutrients, often resulting in irregular patches of thinning, yellowed turf. Nigrospora stolon rot is another fungal infection that causes root decay and prevents moisture absorption. Root-feeding pests, such as white grubs (beetle larvae), also pose a threat by chewing through the fibrous roots just below the soil surface. Heavy grub infestations can completely sever the root system, causing large sections of the turf to lift easily.
Physical and Chemical Stressors
Physical and chemical stressors are equally detrimental. Excessive nitrogen fertilizer encourages rapid top growth at the expense of a strong root structure, weakening the plant. This high nitrogen environment also contributes to thatch buildup, which restricts oxygen and water from penetrating the root zone. High salinity from coastal environments or chemical runoff can impair the roots’ ability to absorb water, mimicking drought stress. Addressing these issues involves calibrating fertilization, managing thatch through aeration, and promptly treating active pest or disease issues.