Bamboo, a member of the grass family Poaceae, is admired for its rapid growth and dense, evergreen foliage. The degree of expansion depends entirely on the specific variety planted. Some species remain tightly clustered while others can rapidly colonize a wide area. Understanding this difference is the first step toward successful cultivation or control, preventing a beautiful screen from becoming a pervasive problem.
The Science of Bamboo Spread
The growth and spread of bamboo rely on a modified underground stem called a rhizome. These structures store energy, allowing the plant to rapidly produce new aerial shoots, known as culms, during the growing season. The two primary growth habits in bamboo are determined by the morphology of these rhizomes.
The most aggressive varieties, known as running bamboos, possess leptomorph rhizomes. These rhizomes are long, thin, and grow horizontally through the soil with an indeterminate growth pattern. A single leptomorph rhizome can travel several feet in a season before a bud develops into a new culm.
In contrast, clumping bamboos feature a pachymorph rhizome system. These rhizomes are short, thick, and curved, with a determinate growth pattern that directs the new culm to grow upward very close to the existing plant. While clumping varieties do expand, their perimeter increases by only a few inches to a foot each year, making them easier to manage within defined spaces.
Identifying Running Versus Clumping Varieties
Distinguishing between the two types is based primarily on the spacing of the culms above ground. Running bamboo creates a diffuse patch with culms spaced far apart due to the long distances the rhizomes travel before emerging.
Clumping bamboo maintains a dense formation, with the culms packed tightly together at the base. A useful identifier for running bamboo belonging to the Phyllostachys genus is the presence of a distinct groove, called a sulcus, running down one side of the culm. Clumping varieties often lack this feature.
A common example is Phyllostachys aurea, or golden bamboo. Conversely, the genus Fargesia represents the majority of cold-hardy clumping bamboos, which are often preferred in residential gardens because of their predictable and non-invasive habit. Selecting the right species based on its rhizome type is the most effective form of preventative control.
Essential Containment and Management Techniques
Managing running bamboo requires a proactive approach. The most reliable containment method involves installing a non-degradable barrier made of high-density polyethylene (HDPE). The material must be at least 60 to 80 mil thick to resist puncture and extend to a minimum depth of 30 inches, as most rhizomes travel in the top two feet of soil.
Installation involves placing the barrier with approximately two inches protruding above the soil line. This exposed edge prevents rhizomes from growing up and over the barrier, where they would then dive back into the soil on the unprotected side. A slight outward angle on the barrier is recommended to direct the rhizomes upward, making them easier to spot and prune.
For established running bamboo, annual rhizome pruning is required. This involves using a sharp spade to sever any rhizomes attempting to cross the containment boundary. Immediately removing any new shoots, or “spears,” that emerge outside the desired area also starves the underground system, as these shoots are the primary way the plant gathers energy for future spread. Eradication is achieved by consistently cutting all culms to the ground and repeatedly removing new shoots over several seasons until the energy stored in the rhizomes is fully depleted.