Monkey grass (Liriope muscari or Liriope spicata) is a tenacious perennial groundcover. It spreads vigorously through a dense network of underground stems known as rhizomes. This extensive root system allows the plant to form dense mats and quickly colonize garden beds, making it difficult to eradicate once established. Successfully killing monkey grass requires a multi-step approach that targets both the visible foliage and the subterranean rhizomes.
Mechanical Removal and Natural Methods
Eradication efforts can begin with manual removal, which is physically demanding but provides an immediate, chemical-free solution. The challenge lies in the plant’s rhizomatous root structure, which must be entirely removed to prevent the plant from regenerating. Simple hand-pulling is generally ineffective because the tough roots tend to snap off, leaving viable fragments in the soil.
A sharp spade or soil knife is the preferred tool to dig out the entire clump, ensuring you lift the root ball and surrounding soil. It is critical to follow the spreading runners and remove every piece of the rhizome, including the small, tuber-like swellings that store energy. All plant material must be removed from the site, preferably bagged and disposed of, as even small remnants can sprout new growth.
For large, established areas, physical barriers can be used to starve the plant of light, a process known as smothering or solarization. Covering the affected patch with thick, opaque plastic sheeting or layers of cardboard and mulch will block sunlight, depleting the energy reserves in the roots. This method requires patience, as the covering must remain in place for at least one full growing season to achieve full eradication.
Chemical Options for Eradication
When mechanical methods are impractical, systemic herbicides offer the most direct path to killing the root system. General broad-leaf weed killers are often ineffective because Liriope is botanically a member of the lily family, not a true grass, and its tough leaves resist absorption. A non-selective, systemic herbicide is required to travel from the foliage down into the rhizomes.
Products containing Glyphosate are the most commonly recommended choice for penetrating the plant’s defenses and killing the underground structures. This chemical is non-selective, meaning it will kill any plant it contacts, necessitating careful, targeted application to avoid harming desirable nearby landscaping. Application should be performed when the monkey grass is actively growing to ensure maximum absorption and translocation to the roots.
The most effective time for treatment is late summer or early fall, as the plant is preparing for dormancy and actively drawing nutrients down to its root system for storage. This downward movement of sap pulls the systemic herbicide deep into the rhizomes, maximizing the kill rate. Repeat applications, often two to three treatments spaced several weeks apart, are usually necessary to kill any surviving growth. Always adhere strictly to the product label instructions regarding concentration, application rates, and safety precautions.
Follow-Up Strategies to Prevent Regrowth
Successful eradication is only the first step, as monkey grass is notorious for its ability to regrow from overlooked root fragments. Long-term management begins with continuous monitoring of the treated area for several seasons, especially during the spring and early summer when new shoots are most likely to emerge. Any new sprouts must be immediately removed by digging or spot-treating with a non-selective herbicide before they can re-establish a viable root system.
To prevent re-invasion, installing a physical root barrier is a highly effective measure. This edging should be buried at least 12 to 18 inches deep along the border of the formerly infested area to block the lateral spread of rhizomes. After the monkey grass is confirmed dead, the soil should be prepared for replanting by incorporating compost or other amendments to improve the growing environment for new groundcover species.