Bamboo’s reputation for aggressive spreading causes significant concern for homeowners and gardeners. Whether bamboo roots are invasive depends entirely on the plant’s specific growth habit. Understanding the underground structure of the plant is the only way to predict its spread and manage it effectively in a landscape.
Running vs. Clumping: The Key Difference
The difference in bamboo behavior is determined by the structure of its underground stems, known as rhizomes. Running bamboos, classified as leptomorph, possess long, slender rhizomes that grow horizontally and aggressively away from the parent plant. These rhizomes can travel many feet in a single growing season, sending up new canes, or culms, far from the original planting site. Genera like Phyllostachys are considered invasive due to this growth pattern.
Clumping bamboos, conversely, are classified as pachymorph, featuring short, thick rhizomes that grow in a tight, U-shape. This structure causes the new culms to emerge immediately adjacent to the existing ones, resulting in a dense, compact clump. The expansion of a clumping bamboo, such as those in the Fargesia genus, is slow and predictable. They typically expand the clump’s diameter by only a few inches annually.
Containment Strategies for Running Bamboo
For those who choose to plant running bamboo, containment requires the installation of a specialized physical barrier. The most effective material is high-density polyethylene (HDPE) sheeting, which should be at least 60 to 80 mil thick to withstand the pressure of the growing rhizomes. The barrier must be installed in a trench dug to a depth of 24 to 30 inches, sufficient to block the shallow-growing rhizomes.
The barrier must protrude 2 to 4 inches above the soil line after backfilling the trench. This above-ground lip prevents the rhizomes from growing up and over the barrier, a phenomenon known as “jumping.” Annual maintenance is necessary, requiring the gardener to inspect the perimeter and cut any rhizomes that attempt to cross the barrier’s edge.
An alternative containment method involves annual or bi-annual root pruning around the perimeter of the planting area. Since running bamboo rhizomes typically grow in the top 5 to 12 inches of soil, a sharp spade can be driven into the ground to sever any outward-spreading rhizomes. This technique requires consistent vigilance during the active growth period from mid-summer through fall.
Eradication: Removing Unwanted Bamboo
One non-chemical approach is the starvation method, which involves repeatedly cutting down all new shoots, or culms, as soon as they emerge. This process prevents the plant from photosynthesizing and replenishing the energy reserves stored in the underground rhizome network. The starvation method must be maintained for at least one to three seasons to fully deplete the rhizomes.
For a faster, though more labor-intensive, solution, physical removal involves digging out the entire rhizome mass. This often requires heavy equipment like a mini-excavator for large, dense patches. Every single fragment of rhizome must be removed to prevent regrowth.
Chemical treatment is a last resort and is most effective when applied directly to the plant’s vascular system. A non-selective herbicide, such as glyphosate, should be applied immediately to the freshly cut culm stumps. The bamboo seals the cut quickly, so the herbicide must be painted onto the stump within minutes to ensure it is absorbed and translocated throughout the rhizome system.