Zoysia grass is a popular, warm-season turf choice known for creating a dense, luxurious lawn that can withstand heat, drought, and heavy foot traffic. This grass is highly valued for its ability to form a thick, carpet-like surface that naturally outcompetes many common lawn weeds. However, the same vigorous growth that makes Zoysia desirable leads many homeowners to question its nature, often labeling it as an “invasive” species. The turf’s tendency to rapidly expand beyond its intended boundaries is a common frustration for those trying to maintain clear garden beds or property lines.
Defining Aggressive Growth vs. Invasive Species
The confusion surrounding Zoysia grass stems from a misunderstanding of scientific terminology, as the difference between an aggressive plant and a truly invasive one is significant. By legal and scientific definition, an invasive species is non-native to a specific ecosystem and causes environmental or economic harm. This harm involves disrupting natural ecosystems, outcompeting native plants, and often being regulated by government bodies like the USDA.
Zoysia grass, native to Asia, does not meet the criteria for an ecologically invasive species in most regions. It is classified as an aggressive turfgrass, meaning it spreads vigorously within a cultivated landscape setting, such as a residential lawn. Aggressive plants are often desirable in a turf context because their spreading nature quickly fills in bare patches and creates a strong sod. The issue of its spread is generally limited to the property line or adjacent flower beds, not a threat to local biodiversity or native habitats.
The Mechanisms of Zoysia Grass Spread
The specific biological structures Zoysia grass uses define its aggressive growth habit. This turfgrass utilizes two distinct types of lateral stems to colonize new ground. The first are stolons, which are modified stems that creep horizontally along the soil surface. These above-ground runners produce new roots and shoots at their nodes, allowing the grass to expand rapidly across the surface of the lawn and into nearby areas like sidewalks or driveways.
The second, more challenging method of spread is through rhizomes, which are modified stems that grow horizontally beneath the soil surface. These subterranean runners are particularly effective because they are hidden and protected from regular mowing. Rhizomes can travel considerable distances underground before sending up a new shoot, often popping up unexpectedly in adjacent flower beds or neighboring lawns.
Containment and Management Strategies
Because Zoysia’s spread is driven by both above and below-ground runners, effective management requires a two-pronged approach focused on maintenance and physical barriers.
Physical Barriers
One of the most effective strategies is the installation of a physical barrier along borders, such as landscape edging or curbing. This barrier must be buried deep enough to intercept the underground rhizomes, with a recommended depth of at least four to six inches. Steel, plastic, or concrete edging should be placed vertically to block the horizontal growth of these underground stems.
Maintenance Practices
Maintenance practices can also significantly regulate the density and vigor of the turf. Zoysia naturally produces a thick layer of organic matter between the soil and the green blades, known as thatch. If this thatch layer exceeds half an inch, it can impede the movement of water and nutrients while providing a medium for the stolons and rhizomes to thrive. Vertical mowing, or dethatching, should be performed in the early summer after the grass has fully greened up to break up this layer and reduce the overall density of the turf.
Chemical Control
Targeted control through the selective use of non-selective herbicides can be used along border areas where the grass has already encroached. A non-selective herbicide, which kills any plant tissue it contacts, should be applied carefully as a spot treatment to Zoysia runners extending into flower beds or along concrete edges. This method requires precision to avoid damaging desirable plants nearby. Additionally, applying a pre-emergent herbicide in the spring and fall can help control unwanted weeds in the turf, ensuring the Zoysia remains the dominant, dense grass.