Bamboo has earned a complicated reputation among gardeners due to its rapid growth and aggressive spreading habits. This polarizing view often stems from a misunderstanding that all bamboo species behave the same way. The reality is that the term “bamboo” encompasses hundreds of species, and their potential for invasiveness is determined by their distinct growth patterns. The central question is whether clumping bamboo poses the same threat as its running counterpart. This difference in underground structure is the definitive factor in whether a bamboo plant remains manageable or becomes an aggressive invader.
The Critical Distinction: Clumping Versus Running Bamboo
The difference between a manageable and aggressive bamboo plant is found in its underground stem structure, known as rhizomes. Bamboo species are categorized into two types based on these structures: running and clumping. Running bamboo uses leptomorph rhizomes, which are long and thin, spreading aggressively over significant distances each year. This structure is responsible for the plant’s reputation for invasiveness, with some species extending many feet from the parent plant in a single season.
Clumping bamboo possesses pachymorph rhizomes, which are short, thick, and U-shaped. This shape causes them to curve upward almost immediately after growing out. This upward turn forces the development of new canes, or culms, close to the original plant. Because the growth tip converts quickly into a new culm, the root system is incapable of traveling great distances. This biological constraint means clumping bamboo is non-invasive and maintains a tight, predictable footprint.
How Clumping Bamboo Spreads
While clumping bamboo is non-invasive, it still expands its footprint over time at a controlled and predictable rate. The pachymorph rhizomes create a dense, circular mass of culms that slowly increase in diameter. This expansion typically increases the clump’s radius by only 2 to 6 inches annually. This slow growth rate allows homeowners to easily predict the plant’s mature size and manage its footprint.
The expansion is driven by new shoots emerging at the perimeter of the existing clump, causing the plant to widen gradually. New rhizomes develop close to the base of the previous year’s growth, resulting in a continuously dense clump where the culms are tightly packed. Over several years, this process creates a widening circle of canes, with the oldest canes occupying the center. The predictable nature of its spread ensures clumping varieties will not suddenly appear far from the main plant.
Practical Management and Containment
Managing the size of clumping bamboo is a straightforward process focused on limiting the outward expansion of the clump. Before planting, choose a location that can accommodate the plant’s mature diameter, which ranges from 2 to 10 feet depending on the species. For long-term containment, a simple annual intervention is often sufficient to maintain a desired boundary.
Root Pruning and Division
Homeowners can perform root pruning by using a sharp spade to slice through the outer edge of the clump’s root mass. This is best done in the late summer or fall when new shoot growth has slowed, effectively severing peripheral rhizomes. If a clump becomes too large or dense, it can be physically divided to control its size. This involves digging up a section of the clump, including the culms and the attached root ball, and separating it from the main plant. Removing new shoots as they emerge at the perimeter during the growing season is another effective way to keep the plant contained.