Monkey Grass, a common name used for plants in the genera Liriope and Ophiopogon, is a popular groundcover frequently used in landscaping. These plants are valued for their evergreen foliage, tolerance for shade, and general hardiness. However, their tendency to spread aggressively often leads gardeners to question their invasive potential. The term “Monkey Grass” encompasses several species with distinct growth habits, and understanding these differences is the first step toward managing their spread. This article will explain the biological reasons behind the plant’s reputation and provide practical strategies for controlling its growth.
Identifying Monkey Grass and Defining Aggression
The plants commonly called Monkey Grass or Lilyturf belong primarily to two genera: Liriope and Ophiopogon. The most frequent species encountered are the clumping Liriope muscari and the running Liriope spicata, along with Ophiopogon japonicus, often known as Dwarf Mondo Grass. These plants originated in East Asia, but not all display the same level of growth aggression.
It is important to distinguish between ecological invasiveness and horticultural aggression. Ecological invasiveness describes a non-native species that escapes cultivation and causes harm to native ecosystems. Liriope spicata is increasingly recognized as an emerging invasive species in certain regions, displacing native plants in wild spaces.
Horticultural aggression refers to a plant that spreads rapidly within a managed landscape, becoming difficult to contain. While Liriope muscari and Ophiopogon japonicus are relatively well-behaved clumpers, the reputation for being “invasive” primarily stems from the highly aggressive nature of Liriope spicata.
Biological Mechanisms of Spreading
The spreading behavior of Monkey Grass is directly related to the different types of modified stems these plants produce for vegetative propagation. These underground structures allow the plant to create clones of itself away from the main crown. The species known as clumpers and those known as runners utilize these mechanisms differently, which accounts for their varying degrees of aggression.
The less aggressive species, like Liriope muscari, primarily expand slowly by producing very short, thick underground stems called rhizomes. These rhizomes grow horizontally but stay close to the parent plant, leading to a gradual increase in the size of the original clump. While the clump expands, it retains a relatively contained shape, making it easier to manage and divide manually.
The highly aggressive species, especially Liriope spicata, utilize a more efficient and far-reaching form of underground stem, often referred to as stolons or creeping rhizomes. These structures are typically more slender than the clumping rhizomes and travel rapidly away from the mother plant. New plant crowns emerge at nodes along these traveling stems, allowing the plant to rapidly colonize a wide area.
Managing Aggressive Growth in the Garden
Controlling the aggressive spread of the running varieties of Monkey Grass, particularly Liriope spicata, requires a vigilant and multi-faceted approach. For prevention, the most effective strategy is to select the right plant variety before planting. Choosing clumping species like Liriope muscari or Ophiopogon japonicus will largely eliminate the issue of rapid lateral spread.
Physical Containment
If managing an established, aggressive patch, physical containment is the most reliable long-term solution. Installing a solid root barrier, such as metal or heavy-duty plastic edging, can block the underground runners from escaping the designated area. This barrier must be sunk into the ground to a depth of at least 18 inches to prevent the creeping rhizomes from simply growing underneath.
Mechanical Removal
For existing infestations, regular mechanical removal and division are necessary to thin the planting. This involves using a sharp spade to sever the runners at the edges of the patch and digging out the entire root sections that have spread into unwanted areas. This process must be done carefully to ensure all pieces of the underground stems are removed, as fragments can resprout quickly.
Chemical Control
In cases of severe, widespread patches, chemical control may be the only practical option, but it requires caution. Herbicides containing glyphosate can be effective, but the waxy leaf coating of Liriope makes penetration difficult. Applying the herbicide after mowing the foliage short and adding a non-ionic surfactant to the mixture can improve its effectiveness. Multiple applications over several seasons are often necessary to fully eliminate a large, established patch of the running variety.