The flowering of a bamboo is an intriguing phenomenon. A phenomenon not because bamboo produces any spectacular flowers... but a phenomenon because it is a unique and very rare occurrence in the plant kingdom. Most bamboos flower once every 60 to 130 years depending on the species!! The long flowering intervals are largely a mystery and still astounds many botanists today with no definitive explanation.
However, not all bamboos exhibit the same flowering characteristics or patterns. Depending on the species, a bamboo can exhibit either gregarious flowering, sporadic flowering or annual flowering.
Gregarious flowering is the most impressive pattern of bamboo flowering. Gregarious flowering is when all populations of a particular species of bamboo flowers all at once. For most species of bamboo, this can happen at intervals anywhere between 60 to 130 years. This flowering cycle is genetically pre-programmed into each species. Once a species reaches its life expectancy, the bamboo will flower and produce seeds. When a bamboo flowers gregariously, it expends a tremendous amount of energy producing flowers and seeds. The mass flowering stresses the bamboo to such an extent that it will die. A particular species can flower and die worldwide, regardless of the geographic location. This means that the same plant in North America will flower and die at roughly the same time (for the most part) as the same plant in Asia!! Most bamboos are simply divisions taken from a mother plant at some point (unless if grown from seed). These divisions are re-divided over time and shared across the world. Although the divisions are geographically in different locations, they still carry the same genetic makeup. That means your bamboo can pretty much be older than you!!
Sporadic flowering is when bamboo flowers sporadically or intermittently. Sporadic flowering is typically brought on by environmental factors rather than genetics. Unlike Gregarious flowering, Sporadic flowering does not happen on a mass scale and the bamboo seldom dies after flowering. It typically occurs on an individual or a group of plants from a localized area. Some species (ie. Phyllostachys Elegans in the U.S.) have been noted to flower sporadically every year for over 10 years. Phyllostachys edulis ‘Moso’ in China seems to always be flowering sporadically.
Although not the norm, it must be noted that there are a few species of bamboo (mostly Schizostachyums) that do indeed flower annually. With these particular species, the bamboo can flower annually with no effect on the parent plant itself. This flowering cycle is known as Annual flowering.