Invasive grass species are plants that were not originally part of a local ecosystem, and they spread aggressively, often harming desired plants and natural landscapes. They are difficult to control because of biological advantages like deep root systems and specialized underground or above-ground runners. These plants rapidly choke out native vegetation or desirable turf by monopolizing resources such as water, light, and nutrients. Successfully eliminating these invaders requires a targeted, multi-step plan that addresses their unique methods of spread.
Identifying the Invader
Effective removal begins with correctly identifying the specific grass species, as its growth habit dictates the best control method. Invasive grasses typically spread in one of two ways: via stolons (above-ground runners that root at the nodes) or via rhizomes (subterranean stems that send up new shoots). Bermuda grass, for example, is aggressive because it uses both stolons and rhizomes.
Other common perennial invaders, such as Quackgrass and Johnson grass, rely on tough, deep-reaching rhizomes, making physical removal challenging. Annual invasive grasses like Crabgrass have a sprawling, bunch-type growth habit and reproduce by seed rather than relying on runners. Understanding this distinction is the first step toward choosing the appropriate removal technique.
Non-Chemical Removal Techniques
For homeowners who prefer to avoid chemical treatments, mechanical and cultural controls offer effective, albeit labor-intensive, solutions. Manual removal is the most direct method, but it must be thorough, requiring careful digging to ensure every fragment of the rhizome or stolon is removed. If even a small piece of a runner-producing grass remains, it can quickly regenerate into a new plant. Therefore, the entire infested area must be excavated to a significant depth.
Smothering and solarization are cultural controls that leverage sunlight and heat to kill the grass and its seeds. Smothering involves covering the area with thick material like cardboard or black plastic sheeting to block out sunlight, depriving the grass of the energy needed for photosynthesis. This process is slower and relies on exhausting the plant’s energy reserves over several months.
Solarization works more quickly by using clear plastic sheeting to trap solar radiation, superheating the moist soil underneath to temperatures that can exceed 140°F. The soil should be tilled, moistened, and then covered with clear plastic for at least four to eight weeks during the hottest part of the summer. This heat sterilizes the top six to twelve inches of soil, killing seeds, surface roots, and rhizome fragments.
Strategic water management can stress certain invasive species. While deep-rooted invaders like Bermuda grass are tolerant of drought, withholding water can weaken less drought-adapted grasses, making them more susceptible to manual removal or follow-up treatments. Reducing irrigation to the minimum required for desirable plants exploits the vulnerability of shallow-rooted competitors, slowing their growth and energy production.
Chemical Control Options
When non-chemical methods are impractical for large infestations or fail against perennial grasses, chemical control options become necessary. Herbicides are categorized as either selective or non-selective, and choosing the correct type is important for success and protecting surrounding plants. Selective herbicides target specific plant types, often killing broadleaf weeds without harming desirable turfgrass. However, they are generally less effective when the invasive plant is also a grass species.
Non-selective, systemic herbicides, such as those containing glyphosate, are the most reliable option for eliminating aggressive perennial grasses. Glyphosate works by inhibiting the EPSP enzyme in the shikimate pathway, a process essential for the synthesis of aromatic amino acids in plants. This systemic action allows the chemical to be absorbed through the leaves and translocated throughout the plant, effectively killing the rhizomes and roots.
Timing the application is a factor for success with systemic herbicides. The chemical must be applied when the grass is actively growing, typically when temperatures are between 65°F and 85°F. This allows the plant to rapidly move the herbicide from the foliage to the root system. Applying the herbicide in the late summer or fall is effective for perennial species, as the plant is moving energy reserves down to its roots in preparation for winter dormancy, drawing the chemical into the storage organs.
Before any application, read and follow all label instructions regarding concentration, application rate, and safety precautions. Non-selective herbicides will kill any plant they touch, requiring careful spot-treatment or the use of a spray shield to prevent drift onto desirable plants. Since this method results in a complete kill, the treated area will need to be replanted after the invasive grass has died off.
Long-Term Prevention and Site Restoration
Eradicating invasive grass requires proper site restoration and prevention of re-establishment. All removed invasive plant material, especially rhizomes, stolons, and seed heads, must be disposed of properly to prevent re-infestation. These materials should never be placed in a compost pile, as fragments can survive the composting process and spread the invader.
The safest disposal method is to place the debris in thick, sealed plastic bags and send it to a landfill, where the material cannot regenerate. Preventing spread from neighboring areas requires installing a physical barrier, particularly for rhizomatous grasses like Bermuda grass. Edging made of durable metal or rigid plastic should be installed vertically at a depth of at least eight inches to block the underground runners from creeping into restored areas.
After the invader is removed, soil health must be addressed to encourage the growth of competitive, desirable plants. Tilling in organic matter, such as compost, improves soil structure and provides nutrients for new plantings. The final step is planting dense, fast-establishing ground cover or bunch-type turfgrass to occupy the cleared space, which out-competes any remaining invasive seeds.