Bamboo is a plant family often desired for its rapid growth and dense foliage, but it carries a reputation for aggressive spread that can quickly overwhelm a garden space. This invasiveness is not a universal trait; the family is divided into two distinct groups based on their underground growth habits: running and clumping. Running bamboos are responsible for the plant’s reputation, sending out long, far-reaching underground stems that sprout new canes many feet away from the original plant. Clumping bamboos offer the same ornamental appeal without the aggressive spreading behavior, growing in dense, manageable circular forms, making them a safe and attractive choice for contained garden beds and landscapes.
Understanding Rhizome Structure
The difference between a spreading and non-spreading bamboo comes down to the structure of its underground stem, known as a rhizome. Running bamboos possess a leptomorph rhizome system, which is long, thin, and travels horizontally through the soil. These rhizomes have buds that can develop into either new rhizomes or new upright canes, called culms, allowing them to rapidly colonize a wide area, sometimes spreading up to 20 feet in a single growing season.
Clumping bamboos, in contrast, utilize a pachymorph rhizome system. These rhizomes are short, thick, and curve upward near the main plant mass. New culms can only form at the very tip of the pachymorph rhizome, which forces the growth to remain close to the existing clump.
This pachymorph structure means the plant expands slowly outward in a dense, circular formation. The result is a predictable, manageable footprint that typically expands only a few inches to about a foot in diameter per year. Understanding this fundamental difference is the first step in selecting a species that will not spread aggressively beyond its intended area.
Identifying Clumping Species
The most reliable way to ensure a bamboo will not spread is to focus on specific genera that are naturally clumping. The genus Fargesia is the most well-known and cold-hardy group of non-spreading bamboos, often tolerating temperatures far below freezing. These temperate clumpers are popular for their graceful, fountain-like growth habit and delicate foliage, making them excellent choices for hedges and screens.
Specific examples of reliable clumping species include:
- Fargesia murielae, often called umbrella bamboo
- Fargesia nitida, known as blue fountain bamboo for its attractive blue-purple culms
- Fargesia robusta, valued for its sturdier, more upright canes and recommended for privacy screening
- Bambusa multiplex (‘Alphonse Karr’ or ‘Hedge Bamboo’), suitable for warmer climates
- Bambusa oldhamii (Oldham’s bamboo), another reliable clumper for warmer regions
When purchasing, a simple visual check can help confirm the plant’s growth habit, as clumping varieties will have a dense mass of culms very close together at the base. Avoid any bamboo labeled with the genus Phyllostachys, as these are the most common and aggressive running types. Choosing a species from the reliable clumping genera eliminates the need for expensive, labor-intensive root barriers that running varieties require.
Maintenance for Contained Growth
While clumping bamboos will not invade neighboring areas, they still increase in size over time and require occasional management to maintain a specific footprint. To keep the clump within its boundaries, a simple root-pruning technique can be performed every few years.
This containment involves using a sharp spade to cut through the rhizomes at the edge of the desired growing area. The severed sections of the rhizome can then be dug out and removed. Alternatively, you can simply cut back the outermost culms when they emerge as new shoots, which is often enough to keep the stand in check.
Maintaining the health of the clump involves ensuring consistent moisture, especially during the first year of establishment and during dry periods. Clumping bamboos thrive in well-draining soil, and they benefit from a yearly application of a slow-release fertilizer in the spring to encourage dense foliage growth. Regular pruning of older, dead, or undersized canes helps thin the center of the clump, promoting better air circulation and light penetration.