St. Augustine grass (Stenotaphrum secundatum) is a coarse-textured, warm-season turfgrass highly favored across the southern United States for its dense, appealing appearance. It spreads quickly by above-ground runners (stolons), forming a thick, weed-resistant lawn. While it thrives in full sunlight, it possesses a notable degree of shade tolerance, contributing to its widespread popularity. Understanding this tolerance is key to maintaining a healthy lawn, as success depends on choosing the correct cultivar and applying specific maintenance practices.
St. Augustine Grass Baseline Light Needs
All turfgrasses require light for photosynthesis, which generates the energy needed for growth and survival. In a low-light environment, St. Augustine grass’s photosynthetic rate drops, resulting in reduced growth and thinning of the turf canopy. This stress causes the grass to become weak and spindly as it stretches its blades to maximize light absorption.
Common varieties, such as ‘Floratam’ and ‘Raleigh,’ typically require a minimum of four to six hours of direct sunlight daily to maintain a dense, healthy stand. This requirement can sometimes be met by heavy, filtered light, often described as dappled shade. Areas receiving less than this minimum will show signs of decline, including decreased density, paleness, and increased susceptibility to disease. True deep shade (less than four hours of direct light) generally cannot sustain common St. Augustine grass long term.
Cultivars Optimized for Shade Tolerance
The most significant factor for growing St. Augustine grass in shade is selecting a shade-tolerant cultivar. These specialized varieties are bred to maintain better density and color under reduced light compared to common types like ‘Floratam.’ The ‘Palmetto’ cultivar is frequently cited for its superior performance, often thriving with only three to four hours of direct sun.
Other notable shade-tolerant varieties include ‘Seville,’ ‘Bitter Blue,’ and ‘CitraBlue,’ all offering improved performance in partial shade. ‘Seville’ is a dwarf variety known for its fine texture and dark blue-green color. While improved, shade tolerance does not eliminate the need for light entirely; even the best varieties will eventually thin out and fail in areas of constant, deep shade.
Specialized Maintenance for Shaded Lawns
Growing St. Augustine grass in a shaded area requires modifying standard lawn care practices to support the grass under stress.
Mowing Height
The primary adjustment is increasing the mowing height, often recommending three to four inches. Maintaining a taller blade maximizes the surface area available to capture limited sunlight, allowing for greater energy production.
Watering
Watering routines must be adjusted to prevent fungal diseases that proliferate in cool, moist, shaded environments. Shaded areas retain moisture longer than sunny spots, increasing susceptibility to conditions like gray leaf spot and brown patch. Deep, infrequent watering is recommended, allowing the soil surface to dry slightly between cycles to discourage fungal growth. Watering should be done early in the morning so grass blades dry quickly.
Fertilization
Fertilization practices differ for shaded turf, which requires less nitrogen than grass in full sun. Excessive nitrogen promotes rapid, weak growth, making leaf blades vulnerable to disease and stress. Applying a slow-release nitrogen fertilizer at a lower annual rate helps maintain turf health without stimulating unsustainable growth. Soil testing can determine if a potassium supplement is beneficial, as potassium improves stress tolerance.
When Shade Requires Non-Grass Alternatives
While St. Augustine grass has the best shade tolerance among warm-season turfgrasses, its limits are reached in areas of deep shade. Deep shade is defined as receiving less than two to three hours of direct sun daily, or being completely blocked by structures or dense tree canopies. In these conditions, even shade-tolerant cultivars will struggle to produce energy and eventually fail, leaving bare patches.
For permanently low-light areas, transitioning to a non-grass ground cover is the most pragmatic solution. Alternatives that thrive in warm climates include Mondo grass (Ophiopogon japonicus) and Liriope (Liriope muscari), which offer a grass-like appearance without high light demands. Other options include shade-loving plants such as sweet woodruff or perennial ferns. Alternatively, applying a thick layer of organic mulch, such as pine straw or shredded bark, creates a clean, low-maintenance landscape bed.