Bamboo is a visually striking and fast-growing plant, often used for landscaping, privacy screens, and hedges. Its rapid growth rate, however, causes concern for many gardeners. The primary issue is understanding the plant’s specific growth habit, which determines how much it will spread. Different varieties have fundamentally different root systems, leading to distinct behaviors. For the popular ornamental Black Bamboo, or Phyllostachys nigra, knowing its root structure is the most important detail before planting.
Clumping Versus Running: Understanding Bamboo Growth Habits
Bamboo species are categorized into two main types based on their underground stems, known as rhizomes. This structure dictates the plant’s spread and its overall footprint. Clumping bamboos use pachymorph rhizomes, which are short, thick, and U-shaped. This results in a tight, slow-expanding cluster of canes that is easily managed.
Running bamboos use leptomorph rhizomes, which are long, thin, and aggressive, growing horizontally beneath the soil surface. These rhizomes extend far from the original plant before sending up new shoots (culms). Running bamboo can quickly colonize large areas if their spread is not contained.
The Growth Habit of Black Bamboo
Black Bamboo (Phyllostachys nigra) is definitively classified as a running bamboo, possessing the vigorous, spreading leptomorph rhizome system. It is not a clumping variety and will aggressively expand its territory if planted directly into the ground without containment measures. Its rhizomes are capable of traveling significant distances, even crossing property lines if left unchecked.
Confusion sometimes arises because other, less common species with black canes, such as Bambusa lako, are true clumpers. When Phyllostachys nigra is young or grown in less-than-ideal conditions, its spread may appear slow initially. However, the plant’s running nature is genetically programmed and will become apparent once the bamboo is established and thriving.
Managing Runner Bamboo in the Garden
Successful cultivation of Phyllostachys nigra requires a dedicated containment strategy from the moment of planting.
Rhizome Barrier Installation
One effective and permanent method is installing a specialized rhizome barrier. This barrier material, often high-density polyethylene (HDPE) plastic at least 40 mil thick, must be installed deep enough to physically block the underground runners. The barrier should be placed 24 to 30 inches deep and angled outward slightly to deflect rhizomes upward. It must also extend two to four inches above the soil line to prevent rhizomes from growing over the top. This creates a complete underground ring, forcing the bamboo to remain within its boundaries.
Regular Root Pruning
A second viable option is regular root pruning, using a sharp spade to sever spreading rhizomes at the perimeter of the desired growing area. This should be done at least once or twice a year, ideally during the active shooting season, by driving the spade into the ground around the entire perimeter. Rhizomes typically grow just a few inches below the surface, generally in the top 2 to 5 inches of topsoil, making them accessible.
Container Growing
Container growing offers the simplest containment solution, as the pot serves as the barrier, making it an excellent choice for smaller yards or patios. Even in a container, the bamboo will eventually become root-bound and require maintenance to prevent rhizomes from escaping through drainage holes. To ensure the plant’s health, the bamboo should be root-pruned and repotted or divided every few years.
Key Characteristics and Basic Care for Black Bamboo
The appeal of Black Bamboo comes from the dramatic color transformation of its canes (culms). New culms emerge vibrant green, but over one to three years, sunlight exposure turns them a glossy, deep black. These slender culms typically reach a mature height of 20 to 30 feet, with a diameter of 1 to 2 inches, providing a dense, upright screen.
Growing Conditions
This species is adaptable and hardy in USDA Zones 7 through 11, though protection may be needed in the coldest parts of Zone 7. For optimal growth and the deepest black color, the plant prefers a location that receives full sun for several hours daily. It tolerates partial shade, but growth may be less vigorous and the culms may not darken as deeply.
Soil and Water Needs
Black Bamboo requires consistently moist, well-draining, and organically rich soil to thrive. It does not tolerate soggy, waterlogged conditions. It is a water-loving plant that should not be allowed to dry out completely, especially during hot summer months. Regular watering and the application of a balanced fertilizer during the growing season support its rapid development and striking color.