Nigra bamboo, also known as black bamboo, or kuro-chiku in Japanese -- all references to its deep ebony colour -- proves a striking addition to your garden. New growth emerges vibrant green but turns a deep ebony by its third year. Native to Taiwan and China, nigra bamboo is cold hardy to freezing temperatures. A "running" bamboo, nigra bamboo quickly spreads through rhizomes burrowing about a foot below the soil surface. While typically growing up to 5 m (16 feet) in height, nigra bamboo's size can be controlled through pruning of existing and emerging new growth.
Choose a fair-weather day in April to May to prune your black bamboo. This is when new culms -- the proper name for bamboo shoots -- emerge. Left unchecked, new shoots can easily reach 5 m (16 feet) in height by June.
Look for new growth emerging from the soil, growing from the rhizomes beneath the surface. These look like springs or corkscrews instead of straight like the older culms. Use sharp hand pruning shears or loppers to cut emergent culms and a third or more of the old growth off at ground level, leaving only the shoots you wish to remain.
Top your nigra bamboo, cutting it to any height you desire. Clip through the culm, just above a node -- the visible joint that bisects the culm, which is actually a rigid membrane of vascular bundles that lends strength to the bamboo shoot -- since cut edges of bamboo culms tend to die back to the nearest node. Alternatively, snap the top off, like you are snapping a pencil in two, to create a clean break. You can cut your nigra bamboo as short as you want, as long as branches still remain. However, topped culms will not grow back.
Trim the branches below the topped bamboo to attain a pleasing shape and avoid a top-heavy look. Make cuts, again, just past the nodes. Balance the branches on either side of the bamboo by trimming equally.
Prune your bamboo similarly each year to maintain the size and look of your bamboo. While individual bamboo shoots live only 10 to 15 years, because of its constant spreading a stand of bamboo may live several decades easily. Bamboo flourishes with consistent trimming and, performed regularly, pruning will make the most of your bamboos' looks.
Remove any dead or dying nigra bamboo culms along with dead branches as part of your pruning procedure. For the best control of new growth, root pruning is suggested. Root pruning involves cutting down and through the rhizomes. Restriction of rhizome growth with barriers is also recommended. Climate zones and planting environment also impact nigra's growth; the bamboo grows shorter in the cold and in containers -- although containers must be frequently replaced as the nigra's rhizomes can tear them apart.