Achieving a dense, thick lawn requires encouraging grass to produce new plants that fill in thin areas. This lateral spread, known as vegetative propagation, is how certain grass types naturally thicken their turf. The process is driven by specialized horizontal stems called runners.
Runners come in two types: stolons, which are above-ground stems that creep along the soil surface, and rhizomes, which are subterranean stems that travel underground. These runners feature nodes that produce new roots and shoots, creating clone plants that contribute to the lawn’s overall thickness.
Confirming Your Grass Type
Identifying your turf is the necessary first step, as the ability to spread laterally is specific to certain grass varieties. Grasses are categorized into spreading (or creeping) grasses and bunching grasses. Spreading grasses, such as Kentucky Bluegrass, Bermuda, St. Augustine, and Zoysia, naturally produce stolons or rhizomes and respond well to density-increasing practices.
Bunching grasses, including Tall Fescue and Perennial Ryegrass, do not produce runners and instead grow vertically from a central crown. If you have bunching grass, manipulating mowing and watering will not cause it to spread. The only way to thicken these lawns is through repeated overseeding.
Optimizing Soil Conditions for Runners
Even spreading grasses need an accommodating physical environment to thrive. Runners, especially below-ground rhizomes, must penetrate the soil easily, and above-ground stolons must make solid contact with the earth to root down. Compacted soil creates a physical barrier that prevents rhizomes from expanding horizontally and limits root system development.
Relieving compaction through core aeration is a beneficial practice. Aeration removes small plugs of soil, allowing air, water, and nutrients to penetrate deeper into the root zone. This process should be timed during the grass’s peak growing season so the turf can recover quickly.
Thatch is another consideration; it is a layer of organic matter that accumulates between the grass blades and the soil surface. If the thatch layer exceeds half an inch, it can prevent stolons from rooting, leaving them vulnerable to drying out. Dethatching involves aggressively raking or vertically cutting the turf to remove this excess material, ensuring stolons can anchor themselves to the soil.
Adjusting Mowing and Watering for Lateral Growth
Mowing height directly encourages grass to prioritize horizontal growth over vertical shoot growth. Maintaining grass blades at the higher end of the recommended range forces the plant to produce more lateral shoots and tillers to capture light. Taller grass blades also create a denser canopy that shades the soil, conserving moisture and maintaining cooler root temperatures.
To minimize stress, observe the one-third rule: never remove more than one-third of the leaf blade length in a single mowing session. Consistent, high mowing encourages the grass to put energy into expanding its root system and producing runners, which thickens the lawn.
The watering strategy should focus on depth rather than frequency to support runner production. Deep, infrequent watering encourages roots to grow downward, resulting in a robust root system. A deep root system provides the energy reserves needed to sustain the development and spread of new stolons and rhizomes.
Providing the Right Nutrients
Fertilization provides the chemical inputs necessary to fuel the vegetative growth required for spreading. Nitrogen (N) is the primary nutrient responsible for promoting shoot and leaf growth, including the development of new runners and tillers. Applying nitrogen during the active growing phase directly supports the energy demands of lateral expansion, resulting in denser turf.
Potassium (K) is also important, as it enhances the grass plant’s ability to tolerate stress from drought, heat, and disease. A plant that withstands environmental pressures can allocate more energy toward producing and sustaining new runners, rather than recovering from damage.
Phosphorus (P) is associated with strong root establishment but is often not needed in high amounts on mature lawns. Apply high-phosphorus fertilizer only if a soil test indicates a deficiency or when establishing a new lawn, as excessive amounts can cause environmental issues. Selecting a slow-release granular fertilizer ensures a consistent supply of nutrients for continuous spreading.