The speed at which a lawn fills in bare patches or thickens into dense turf is a primary concern for many homeowners. This spreading, known as vegetative propagation, refers to the horizontal growth and colonization of the surrounding soil. The rate of this movement is highly dependent on the grass species’s inherent biological mechanisms and the external environmental conditions it encounters. Understanding these two factors helps determine what to expect from your lawn and how to influence its growth.
The Biological Methods of Grass Spreading
The fundamental difference in grass spreading speed lies in the presence or absence of specialized horizontal stems. Grasses achieve lateral growth using one or more of three primary methods.
The fastest-spreading grasses employ stolons, which are above-ground runners that creep along the soil surface. These stems have nodes that root and produce new shoots, creating a new plant a short distance from the parent.
A slightly slower, but more durable, method involves rhizomes, which are horizontal stems that grow beneath the soil surface. Rhizomes also produce new shoots and roots at their nodes, but their underground location offers better protection from environmental stress. Grasses that possess both stolons and rhizomes are typically the most aggressive spreaders.
The third method is tillering, which involves the production of new shoots, or tillers, that emerge vertically from the crown. Grasses that rely solely on tillering, known as bunch-type grasses, do not spread laterally to cover bare ground. Instead, they grow outward in clumps, increasing the density of the existing patch.
Comparing Spreading Speeds of Common Grass Types
The three biological structures translate directly into differences in the spreading capacity of common turfgrasses. Warm-season grasses, which thrive in hot climates, are generally the fastest and most aggressive spreaders.
Bermuda grass is considered the fastest-growing turfgrass, utilizing both stolons and rhizomes. Under optimal conditions, it can spread multiple feet in a single growing season. Zoysia grass also uses both runners but is a moderate spreader, typically colonizing new ground at a rate of six inches to one foot per year. Centipede grass relies primarily on stolons and is known for its slower spread, often moving only about six inches annually.
Cool-season grasses, such as Kentucky Bluegrass, Tall Fescue, and Perennial Ryegrass, exhibit a different spreading profile. Kentucky Bluegrass is the standout spreader in this group, using rhizomes to slowly thicken the turf and recover from damage. Tall Fescue and Perennial Ryegrass are primarily bunch-type grasses that spread minimally through tillering, making them poor choices for quickly repairing large bare areas.
Environmental Conditions That Impact Growth Rate
The inherent speed of a grass species is only realized when external environmental factors are favorable. Temperature is a primary regulator of growth. Warm-season grasses require soil temperatures between 70° and 90°F and air temperatures between 80° and 95°F for maximum spreading. Cool-season grasses grow best when soil temperatures are between 50° and 65°F and air temperatures range from 60° to 75°F.
Soil health and nutrient availability are also major factors, particularly the presence of nitrogen, which fuels the vegetative growth required for runner extension. A lack of nitrogen will severely limit the production and elongation of stolons and rhizomes, slowing the spreading rate. Adequate moisture is also non-negotiable, as the establishment of new roots from the nodes of runners requires consistent access to water.
Sunlight exposure significantly affects the speed of horizontal growth, particularly for aggressive warm-season grasses like Bermuda, which require full sun to thrive. When these grasses are subjected to shade, their spreading rate is suppressed, and the plants become thin as they stretch vertically to seek light.
Techniques to Maximize Lawn Coverage Speed
To encourage the fastest possible spread, homeowners should focus on manipulating the growing environment to meet the needs of the chosen grass type.
Applying a nitrogen-rich fertilizer during the grass’s peak growing season provides the necessary energy to drive the production and extension of runners. For warm-season grasses, this means summer applications, while cool-season grasses benefit most from feeding in the early fall and spring.
Practices that improve soil structure, such as core aeration, are highly effective in maximizing the spread of rhizomatous and stoloniferous grasses. Aeration relieves compaction, allowing runners and roots to penetrate the soil more easily and access water and nutrients.
Mowing practices also influence lateral growth, especially for creeping grasses. Mowing at the lower end of the recommended height range for a species encourages a more prostrate growth habit. This lower cut stimulates the horizontal development of stolons and rhizomes, promoting a denser turf that fills in bare spots more quickly.