St. Augustine and Bermuda are two of the most prevalent warm-season turfgrasses chosen by homeowners across the Southern United States. Both varieties thrive in the region’s long, hot summers, creating dense, attractive lawns. Despite their shared climate preference, these grasses possess different characteristics, which often leads to the question of whether they can coexist. The accidental spread of one variety into a lawn dominated by the other, or a change in a property’s sun exposure, frequently results in a mixed stand. Understanding the conflict between them is the first step in managing a turf area where both are present.
Contrasting Growth Habits and Needs
The incompatibility between St. Augustine and Bermuda grass begins with their growth patterns and environmental requirements. St. Augustine grass spreads exclusively through above-ground runners called stolons, giving it a moderate growth rate. It is notably shade-tolerant, making it a preferred choice for yards with mature trees, and performs best when maintained at a relatively tall height, typically between three and four inches. This grass also requires consistent soil moisture to maintain its health and lush, coarse-bladed appearance.
Bermuda grass, by contrast, is far more aggressive, spreading through both stolons and underground runners known as rhizomes. This dual-spreading mechanism allows it to rapidly colonize bare ground and recover quickly from damage. Bermuda is a sun-loving species, demanding a minimum of six to eight hours of direct sunlight each day to thrive. It maintains its finest appearance when mowed very short, often below two inches, and exhibits a much higher tolerance for drought conditions than St. Augustine.
The distinct maintenance needs of each grass create a conflict when they are planted together. St. Augustine’s preferred mowing height and watering schedule are detrimental to Bermuda grass, while Bermuda’s low, frequent mowing and need for intense sun will quickly stress and thin out the St. Augustine. These opposing cultural requirements mean any attempt to satisfy both varieties simultaneously will ultimately fail to produce a uniform lawn.
The Appearance of a Mixed Lawn
Mixing St. Augustine and Bermuda grass is generally not recommended because the result is a visually inconsistent and patchy lawn. The most immediate contrast is the difference in leaf texture. St. Augustine has broad, flat blades that give the lawn a thick, carpet-like appearance, while Bermuda grass features very fine, slender blades that create a dense, low-cut, finely textured surface.
When these two textures meet, they do not blend but form noticeable, irregular patches that disrupt the uniformity of the turf. The color contrast further emphasizes this patchwork effect, as St. Augustine often displays a deeper, blue-green hue, while common Bermuda grass can be a brighter or lighter green. This visual clash prevents the achievement of a cohesive, manicured aesthetic.
The competition between the two grasses also dictates the final, uneven appearance of the lawn. In sunny areas, the highly aggressive Bermuda grass, with its deep-reaching rhizomes, will aggressively outcompete and displace the St. Augustine. However, in any shaded spots, the St. Augustine will thrive and choke out the Bermuda, which will thin and die in low light. This struggle for dominance results in a lawn that is perpetually uneven, with distinct areas of one variety or the other.
Strategies for Turf Separation
For a homeowner who already has a mixed lawn, establishing a single, uniform turf requires choosing one grass over the other and actively suppressing the remaining variety. The decision should be based primarily on the property’s sun exposure, selecting the variety best suited to the overall microclimate. If the lawn is mostly sunny, Bermuda is the practical choice, while St. Augustine is better for yards with significant shade coverage.
Eliminating St. Augustine from a Bermuda lawn can often be accomplished through cultural practices, as St. Augustine cannot tolerate the low mowing heights preferred by Bermuda. By consistently cutting the entire lawn at a height of one to one-and-a-half inches, the St. Augustine will be severely stressed and eventually recede. The removal of Bermuda from a St. Augustine lawn is a more difficult task due to the Bermuda’s tenacious underground rhizomes.
In cases where Bermuda has invaded St. Augustine, maintaining the St. Augustine at its maximum height of four inches can help shade out the sun-loving Bermuda. For more severe infestations, targeted application of selective herbicides is necessary. Products containing active ingredients like fenoxaprop-P-ethyl can control the Bermuda without severely damaging the St. Augustine. This chemical approach must be followed by cultural practices that promote the desirable grass to fill in the bare areas.