Grass plants exhibit diverse growth habits, and a significant characteristic distinguishing many turf varieties is their method of horizontal expansion. This lateral spreading, often described as having “runners,” is accomplished through specialized stems that allow the plant to colonize bare ground quickly and form a dense, interconnected lawn. Understanding these growth structures is fundamental, as they determine the grass’s ability to self-repair, its tolerance to foot traffic, and the maintenance practices required to keep it healthy.
Understanding Grass Spread Mechanisms
The term “runners” refers generally to two distinct types of modified stems used for vegetative reproduction: stolons and rhizomes. These structures enable grasses to spread horizontally and generate new plants, effectively creating clones of the parent plant. This method of growth is more efficient for turf establishment than relying solely on seed.
Stolons are horizontal stems that creep along the surface of the soil, producing roots and new shoots at the nodes. This above-ground growth allows for rapid colonization of open areas. In contrast, rhizomes are underground horizontal stems that push out through the soil and send up new shoots and roots at their nodes. These subterranean stems act as energy storage organs, aiding the grass’s recovery from environmental stress or physical damage.
Warm-Season Grasses That Use Runners
Warm-season turfgrasses, which thrive in high temperatures, include the most common and aggressive examples of runner-producing varieties. Their spreading mechanisms are the primary reason they form such dense, wear-resistant lawns. The ability to spread quickly helps these grasses outcompete weeds and fill in damaged areas rapidly during their active growing season.
Bermuda grass utilizes both above-ground stolons and underground rhizomes, making it one of the most vigorous and fast-spreading grasses available. This dual system allows Bermuda grass to quickly cover large areas and recover well from heavy traffic. The combination of surface runners and subterranean stems contributes to its reputation for being persistent and sometimes invasive in garden beds.
St. Augustine grass, known for its broad, coarse leaf texture, primarily spreads by thick, robust stolons that creep across the soil surface. These above-ground runners grow quickly, helping the grass establish a dense, carpet-like appearance. It lacks the underground recovery mechanism provided by rhizomes.
Centipede grass also spreads mainly through above-ground stolons, characterized by its slower growth rate compared to Bermuda or St. Augustine. This slower, stoloniferous spread is often preferred for low-maintenance lawns where aggressive growth is a concern.
Zoysia grass utilizes both stolons and rhizomes, similar to Bermuda grass, but its overall growth rate is slower than Bermuda varieties. This combined spreading habit allows Zoysia to form a dense, thick turf that is tolerant of wear. The presence of rhizomes also provides Zoysia with improved cold tolerance and better winter survival compared to purely stoloniferous warm-season grasses.
Cool-Season Grasses and Their Spreading Habits
Most cool-season turfgrasses, which grow best in spring and fall, are classified as bunch-type grasses, meaning they expand primarily by producing new shoots, or tillers, from the base of the plant. Unlike runner-producing grasses, bunch-type varieties such as Tall Fescue and Perennial Ryegrass do not spread laterally to fill in bare spots. If damage occurs, these grasses require overseeding to repair the area.
A notable exception among cool-season turf is Kentucky Bluegrass, which relies heavily on underground rhizomes for its spreading ability. This extensive rhizome network enables Kentucky Bluegrass to form a dense sod and provides a self-repairing capability for athletic fields and lawns. The rhizomes allow the grass to recover from injury and traffic, a characteristic uncommon among its cool-season counterparts.
Another cool-season exception is Creeping Red Fescue, which spreads slowly using short, slender rhizomes. While its spreading habit is not as aggressive as Kentucky Bluegrass, the rhizomes help this grass tolerate low-input conditions, such as shade and drier soils. The subtle, creeping nature of its spread helps it form a tight, fine-textured turf, often used in mixtures with other fine fescues.
Managing Aggressive Growth
The presence of runners, whether stolons or rhizomes, significantly impacts lawn maintenance, particularly due to the grass’s tendency toward aggressive lateral expansion. Regular edging is necessary along sidewalks, driveways, and garden beds to prevent stolons from creeping into unwanted areas. Without this intervention, surface runners will continually colonize adjacent spaces, requiring more effort to maintain defined borders.
The dense growth habit promoted by runners means that certain turf varieties can accumulate thatch, a dense layer of organic material between the soil and the green blades. Stoloniferous grasses like St. Augustine and Zoysia are prone to this issue, as the overlapping runners contribute to the thatch layer. Excess thatch greater than a half-inch prevents water and nutrients from reaching the soil, necessitating periodic dethatching, usually in the late spring or early summer for warm-season varieties.
The self-repairing capability conferred by runners is an advantage, making these grasses well-suited for high-traffic areas. When turf is damaged, the runners quickly grow into the bare spot, regenerating the lawn without the need for manual patching or reseeding. This rapid recovery rate is why rhizomatous and stoloniferous grasses are preferred for active lawns and sports surfaces. However, managing the thatch and controlling the aggressive spread are necessary trade-offs for enjoying a dense, durable turf.