Lemongrass is a tropical herb prized globally for its bright, citrusy aroma and flavor, making it a staple in Asian cooking and herbal teas. The tall, slender, arching green leaves of Cymbopogon citratus create an impressive clump. As this plant thrives in warm, sunny conditions, its vigorous growth habit frequently raises concerns about its potential to take over planting areas. Understanding the specific mechanism of its rapid spread is the first step in successfully managing this productive herb.
Defining Aggression: Is Lemongrass Truly Invasive?
The term “invasive” is a specific classification for non-native species that spread widely, cause ecological harm, and disrupt local ecosystems. Lemongrass, in contrast, is generally not considered truly invasive in most regions where it is cultivated. True invasive plants often spread rapidly via seed, allowing them to travel long distances and colonize natural areas. Lemongrass rarely flowers or sets viable seed when grown outside of its native tropical habitat, which is typically zones 10 and warmer. This lack of seed production prevents it from spreading across wide areas and threatening natural ecosystems. Instead, the herb is classified as “aggressive” because of its method of localized expansion. Its spread is contained to the immediate area of the original planting, though it can overwhelm adjacent plants and garden beds if left unchecked.
Understanding Rhizome Growth and Spread
The aggressive expansion of lemongrass is directly linked to its root structure, which relies on rhizome growth. Rhizomes are specialized, horizontal underground stems that function both as storage organs and as a primary means of asexual reproduction. They allow the plant to continually send out new shoots and roots from nodes along their length. For lemongrass, these rhizomes radiate outward from the central crown, creating new stalks that form a progressively denser, larger clump. This lateral spread causes the plant to increase dramatically in diameter, potentially growing into a specimen up to six feet wide. The rapid formation of these dense root masses is what causes overcrowding and competition with nearby plants in a cultivated setting.
Proactive Planting Strategies for Containment
Preventing the physical spread of lemongrass begins with strategic planting choices made before the plant is established. The most effective containment method is growing the herb in a large container, which naturally restricts the outward growth of the rhizomes. Select a pot that is at least 12 inches across and deep, or use a five-gallon bucket, as the plant can grow between three and five feet tall in a single season. If planting directly into the ground is preferred, a physical root barrier is necessary to manage the aggressive expansion. This barrier can be constructed from durable plastic edging or metal flashing, and it must be installed vertically into the soil around the planting area. For effective containment, the barrier should extend at least 18 to 24 inches deep, preventing the rhizomes from simply growing underneath the edge. When placing the plant, choose a location away from delicate annuals, pathways, or utility lines, allowing for the substantial four-foot spread that the plant can achieve.
Managing Overgrown or Unwanted Patches
For gardeners dealing with an established patch that has exceeded its boundaries, remedial management focuses on physical reduction and division. Hard pruning the foliage, which involves cutting the entire clump back to a few inches above the ground, helps keep the plant tidy and encourages new, tender growth. This seasonal cutback, often performed in late winter or early spring, reduces the plant’s overall size and vigor. To reduce the physical footprint of the root mass, the clump must be physically divided using tools capable of cutting through the dense rhizome network. Dig up the entire plant and use a sharp spade, saw, or even an axe to separate the root ball into smaller, manageable sections. Complete eradication of an unwanted patch requires the thorough removal of the entire root ball, as any small section of rhizome left in the soil can quickly regrow.