Bamboo is often celebrated for its rapid growth and dense, attractive foliage, making it a popular choice for screens and privacy hedges. However, this plant also possesses a reputation for aggressive spread, a characteristic dictated by its underground structure. The term “rhizome” refers to the horizontal, underground stem system that serves as the plant’s means of nutrient storage and vegetative reproduction. Understanding this architecture is fundamental for any homeowner or gardener, as the depth and lateral reach of these rhizomes are the primary concerns for containment.
Understanding the Two Primary Rhizome Systems
The spread potential of any bamboo species is determined by one of two distinct rhizome systems, which dictate whether the plant will form a tight cluster or aggressively colonize an area. This distinction separates the species into “clumping” and “running” types. A rhizome is a specialized horizontal stem, differentiating it from a true root, which grows downward and absorbs water and nutrients.
Clumping bamboo, known scientifically as pachymorph or sympodial, features rhizomes that are short, thick, and U-shaped, with an upward curve at the tips. This morphology causes new culms—the above-ground canes—to emerge immediately next to the existing ones, resulting in a dense, slowly expanding cluster. Clumping varieties are generally non-invasive, preferring to expand their diameter by only a few inches annually under typical conditions.
Running bamboo, classified as leptomorph or monopodial, is the source of the plant’s aggressive reputation. Its rhizomes are long, slender, and grow horizontally away from the parent plant. These rhizomes can travel great distances underground before sending up a new shoot, making running bamboo the primary cause of invasive spread.
Typical Root Depth and Lateral Spread
The depth at which bamboo grows is surprisingly shallow, as the plant does not develop a deep taproot. The vast majority of a bamboo’s spreading rhizomes, particularly those of the running varieties, are concentrated in the top 6 to 18 inches of soil. This shallow concentration is why an effective containment barrier does not need to extend prohibitively deep into the ground.
While the primary rhizomes remain near the surface, the fine, fibrous feeder roots that absorb water and nutrients can extend slightly farther down. These fine root masses may reach depths of 2 to 3 feet, especially in loose soil, but they do not contribute to the plant’s lateral spread. Depth is heavily influenced by environmental factors; rhizomes often stay closer to the surface in moist, rich soil compared to hard or compacted earth.
Lateral spread is where the two types differ dramatically. Running bamboo rhizomes can spread laterally by 5 to 15 feet or more in a single growing season under optimal conditions. This rapid growth rate means an uncontained running bamboo patch can quickly colonize new areas. In contrast, clumping bamboo expands much more predictably, with the overall diameter of the clump increasing by only a few inches each year as new canes emerge tightly around the existing ones.
Essential Containment and Barrier Methods
For homeowners choosing to plant running bamboo, installing a proper rhizome barrier is the only reliable method to prevent aggressive spread. The barrier material should be high-density polyethylene (HDPE) plastic, preferred over metal or concrete because it is flexible and does not rust or crack. This material should have a minimum thickness of 40 to 60 mil to withstand the pressure of the growing rhizomes.
The depth of the barrier is crucial for effective containment and must be installed to a depth of 24 to 30 inches below the soil surface. Equally important is leaving a portion of the barrier protruding 2 to 3 inches above the soil line. This exposed lip prevents rhizomes from growing up and over the barrier, which is a common failure point for improperly installed systems.
To maximize the barrier’s effectiveness, it should be installed with a slight outward angle, tilting the bottom edge toward the center of the contained area. This angle ensures that any rhizomes encountering the plastic are deflected upward, making them visible above the exposed lip for easy removal. Even with a correctly installed barrier, a clear trench should be maintained around the perimeter, and annual root pruning is necessary to sever any escaping rhizomes.
Management of Established and Escaped Bamboo
When bamboo has already escaped containment or an established patch needs removal, the focus must shift to exhausting the underground rhizome network. The most direct method is manual removal, which requires cutting the culms and then digging out the entire rhizome mass. This process is highly labor-intensive, as a mature root ball can be dense and requires heavy tools to break apart and lift from the ground.
Because any small fragment of rhizome left in the soil can regrow, manual removal must be followed by persistent monitoring and removal of new shoots. A less disruptive but slower method is the “mow and starve” technique, which works by continually depleting the energy stored in the rhizomes. This involves cutting all above-ground canes close to the soil and then persistently cutting or mowing any new shoots as soon as they emerge.
The repeated removal of new culms prevents the plant from photosynthesizing, thereby starving the rhizome system over the course of two to three growing seasons. For faster results, chemical treatment using a systemic herbicide like glyphosate can be employed, though it requires careful application. The herbicide is most effective when applied to the fresh cuts of the culms or painted onto the leaves of new shoots, allowing the chemical to be transported directly into the underground rhizome system.