A bamboo barrier, often called a rhizome barrier, is a non-porous physical shield installed underground to manage the aggressive spread of certain bamboo species. Its function is to physically intercept the underground stems, or rhizomes, that allow the plant to colonize new territory. This containment strategy is only successful when the barrier is installed with precision, ensuring no part of the rhizome network can circumvent the material. Success depends on correct depth, material specifications, and installation techniques.
The Difference Between Running and Clumping Bamboo
The necessity of a physical barrier is determined by the specific growth habit of the bamboo. Bamboo is categorized into two types based on its rhizome structure. Running bamboos are defined by their leptomorph rhizomes, which are long, thin underground stems that aggressively shoot horizontally away from the main plant. These rhizomes can travel great distances, making running bamboo the primary reason for barrier installation.
In contrast, clumping bamboos possess pachymorph rhizomes, which are short, thick, and curve upward near the main plant to produce a new cane. This growth pattern results in a slow-expanding, compact group of culms that rarely requires an underground barrier. The specifications discussed for barriers are designed to manage the spreading nature of the leptomorph rhizomes found in running bamboo.
Required Depth and Specifications for Barrier Material
The standard minimum depth for a bamboo barrier is between 24 and 30 inches, which is sufficient to intercept the majority of running rhizomes. Although most rhizomes grow in the top 18 inches of soil, the barrier must be deeper to account for a rhizome’s tendency to turn downward upon encountering the obstruction. In areas with lighter, sandy soils or for vigorous species, the barrier depth should approach 36 inches to ensure complete interception.
The material used must be non-perforated and resistant to puncture. High-Density Polyethylene (HDPE) is the industry standard for rhizome barriers due to its durability and flexibility. Thickness is measured in mils, with a minimum specification of 60 mil necessary for effective containment. For aggressive running bamboo or in very rocky soil, an 80-mil thickness is recommended to withstand the pressure exerted by the expanding rhizomes.
Essential Installation Techniques for Containment
The trench dug for the barrier should be approximately two inches shallower than the barrier material, ensuring the necessary portion remains above the soil line. After digging the trench and clearing it of any existing rhizomes, the barrier should be inserted and positioned at a slight outward angle. This intentional slant encourages any rhizomes that strike the barrier to deflect upward toward the soil surface, rather than burrowing down underneath the material.
The material must protrude between two and four inches above the final soil grade to create a visible lip. This above-ground extension prevents rhizomes from growing up and over the top edge of the barrier. If the barrier material is not a continuous roll, overlapping joints must be securely sealed. This requires overlapping the material by at least 12 inches and bolting the seam together with stainless steel clamps to eliminate any potential gap. Backfilling the trench, especially the bottom portion, must be done with tight compaction to prevent voids that would allow a rhizome to travel downward along the barrier face.
Ongoing Monitoring and Barrier Maintenance
A properly installed rhizome barrier is an effective containment method but is not a permanent, passive solution. Annual monitoring is required to ensure long-term success. The visible two- to four-inch lip must be inspected at least once a year, preferably in late summer or fall when rhizome growth is most active.
This inspection involves clearing away accumulated mulch, leaves, or soil that might have buried the exposed edge of the barrier. Any rhizomes found attempting to grow over the visible lip must be severed and removed. Pruning these wayward rhizomes, often found just beneath the soil surface near the barrier’s edge, is a necessary maintenance task that prevents a containment breach.