Bamboo offers a striking architectural element to any landscape, prized for its elegant, segmented canes and graceful foliage. Plants marketed as “purple bamboo” are highly sought after for their unique color, providing a dramatic contrast against traditional greenery. These distinctive forms can serve as a privacy screen, a standalone specimen, or a dramatic backdrop. Understanding the specific needs of these colorful forms is paramount to cultivating the deep hues.
Identifying the Purple Bamboo Plant
The term “purple bamboo” most commonly refers to Phyllostachys nigra, or Black Bamboo, native to the Hunan Province of China. This bamboo is famous for the color transformation of its culms (rigid, hollow stems). When new culms emerge in the spring, they are vibrant green. The deep, nearly black hue, often described as purple, develops gradually over the first one to three seasons of growth. This darkening is a maturation process where chlorophyll breaks down, allowing underlying pigments to become visible. A less common species sometimes called purple bamboo is Drepanostachyum khasianum, or Purple Jade Bamboo, which features a powdery, grayish-blue culm that can take on violet tones.
Essential Growing Conditions
Achieving the deepest coloration in purple bamboo, particularly Phyllostachys nigra, depends on providing optimal growing conditions, starting with the soil. This bamboo thrives in rich, slightly acidic soil that is both well-draining and moisture-retentive. Incorporating organic matter, such as compost, improves both drainage and the soil’s capacity to hold moisture.
For the color to fully saturate and darken, the plant requires substantial sunlight, ideally at least four hours of direct sun daily. Insufficient light causes culms to remain green or develop only a muted color. Consistent moisture is necessary, as the plant originates from moist forest understories and leaves will curl if dehydrated.
During the active growing season, consistent watering is more beneficial than infrequent, deep soakings. Once established, the bamboo benefits from a high-nitrogen fertilizer (e.g., 20-5-10 NPK ratio), applied two to three times per growing season. This supports the vigorous growth of new culms that will develop the mature color. Maintain a thick layer of organic mulch, two to four inches deep, over the root zone to conserve moisture and provide slow-releasing nutrients.
Managing Spread and Containment
Phyllostachys nigra is classified as a running bamboo, meaning it spreads aggressively via long, underground stems called rhizomes. These rhizomes grow horizontally, often shallowly, and can travel many feet from the parent plant before sending up new culms. This growth habit necessitates proactive containment measures to prevent unpredictable spreading.
The most reliable containment method involves installing a physical root barrier made of durable, high-density polyethylene plastic (100 mil thickness recommended). The barrier must be installed vertically to a depth of at least 24 to 30 inches. Leave about two inches exposed above the soil line; this lip ensures that rhizomes attempting to grow over the barrier are visible and can be pruned.
Alternatively, the plant can be confined to a large container or a deep trench can be dug around the bamboo. Annual maintenance is necessary to inspect the area and prune any escaping rhizomes before the main shooting season.
Seasonal Maintenance and Common Issues
Pruning mature culms maintains the aesthetic appeal of the bamboo and improves overall health. Older canes, typically three years or older, should be thinned out at ground level to encourage better air circulation and make space for new shoots. Removing approximately one-third of the oldest culms annually is a guideline for maintaining a dense, healthy grove.
Bamboo is an evergreen grass, and a natural leaf drop occurs in the spring, causing some leaves to turn yellow before new growth replaces them. Phyllostachys nigra is cold-hardy down to about 0°F, but a thick layer of mulch is beneficial during the first winter to protect the root system. Topping permanently sets the cane’s height and controls the plant’s overall size.
Pest issues are minimal, but bamboo mites and scale insects can occasionally cause problems. Mites cause stippling and yellowing on the leaves. This damage can be managed by applying horticultural oil or by encouraging natural predators. Proper spacing and thinning also mitigate pest problems by ensuring good air flow.