Bamboo commonly grows in clumps. A stalk of bamboo will grow from a seed or rhizome. The stalk produces rhizomes and roots beneath the soil. New stalks appear around the first stalk and within eight years, the original stalk has reached its maturity. The soil beneath the topsoil may become so thick with roots and rhizomes that it is impossible to dig without the aid of saws and picks. This formation of a clump through spreading rhizomes is partly responsible for the classification of bamboo as a grass. Bamboo is one of the world's fastest growing plants and under optimum conditions, may grow almost four feet in a day--fast enough that some say you can hear it growing.
Many bamboo species flower only when environmental changes threaten the clump. The entire clump will cease growing or producing leaves--it puts all its stored energy and food into flowering and producing seeds. The mature seeds fall to the ground and germinate in as little as three to five days. The clump and all its rhizomes, depleted of food of and energy, dies. A few species flower yearly, although sparsely, and produce a few seeds without dying. These two factors contribute to the scarcity of seed available to gardeners and production growers alike. If your bamboo flowers, it may signal that the clump is going to die. Plant the seeds as soon they are mature. Bury the bulb end of the seed that contains the embryo.
Bamboo is a grass and easily expands its clumps through rhizomes. Rhizomes grow from other rhizomes and send shoots up to the surface, and roots down into the ground. The shoots become new stalks, fed by the root system growing below the rhizomes. By the time the stalks are one year old, the rhizome attached has sent off other rhizomes to grow more shoots. The rhizomes are intertwined with the rhizomes from other shoots; they are all interconnected and interdependent. The stalks (called culms), rhizomes and roots all grow and form the same way. The tip grows out and forms a new node, which is covered in a sheath that is quickly replaced. The nodes start out very close to each other and as the plant grows, each node expands along its length and girth until the plant reaches maturity.
In a process called layering, one-year-old stalks are bent over and buried in a shallow trench--new shoots grow from the stalk's nodes. Divide clumps into smaller clumps by digging around the edges so that only the newest rhizomes are taken from the edges of the existing clump. The older rhizomes near the center of the clump will produce very few or no new rhizomes. Taking vegetative cuttings is another method of propagation with mixed results, depending on the age of the stalks and the species of bamboo. Some species are very aggressive, producing many fast growing rhizomes. These species make poor landscape plants, taking over a yard in a short time.