Bamboo

There was a flurry of excitement in the Master Gardener office this past July. After an unusually large number of questions about bamboo, a local gardener brought in a bamboo branch from her garden, and it was in flower! A bit of research indicated that this is quite a rare occurrence and it piqued interest in this horticultural sub-family, so Al asked me to feature it in September. Little did I know where this would take me…what a fascinating subject! One of the first things I learned is that bamboo stems are properly called “culms,” and the flower is technically an “inflorescence.” The culms grow only in height, never in width; they retain the same diameter as when they first emerge from the ground. And flowering is very rare; some types bloom once every 15 years, but others may take more than 100 years to flower.

Flowering is sometimes noted with dread, because many bamboos are monocratic; that is, they flower just once. So much energy is required from the plant that it is likely to die. Some sources hold that one harbinger of bloom is the inability of the roots to take up nutrients; growth stops and flowering occurs. There are reputed to be two kinds of flowering: sporadic, in which a single plant, culm, or branch bears flowers; and gregarious, when all plants of a particular clone, variety, or species flower worldwide at the same time. In cases of gregarious flowering, it follows that entire varieties may die once they flower; and there is an enormous amount of information available about how to rejuvenate bamboo that has flowered, and how to prepare for eventual flowering by vegetative propagation. One of the curious aspects of bamboo is that seeds are seldom true to the parent plant; and even vegetative propagation may result in a different plant form. So there is much fear that gregarious flowering can result in the demise of an entire variety of bamboo. Dedicated bamboo people regularly track inflorescence activity in a particular species, variety, or clone, asking like-minded folks to report sightings. The specimen brought to our office was identified as Phyllostachys flexuosa; the same species bloomed in Portland last year. Divisions made then are thriving and have not repeated the bloom cycle, except for one culm that was not removed from the divided rhizomes. There are predictions that P. dulcis might bloom soon, based on intervals between flowering recorded in the past. This species, grown successfully in the Northwest, has culms that are three inches in diameter.

There are several different genera of bamboo, and the naming of species and varieties is far from consistent. Botanists have had trouble with a standard taxonomy for bamboo. This is evidently due to several factors, including the fact that classification is often based on flower form and as noted, the interval between flowering of some bamboos exceeds the life span of most botanists. Also contributing are the lack (until recently) of open communication between botanists in different political systems, and the innate tendency of bamboo offspring to vary in form from parental stock. (For those of you who like to collect such tidbits, Gelidocalamus fangianus is the universally accepted name of the giant pandas’ primary food source.) Suffice it to say that there are two main types of bamboo: clumping and spreading, defined by the way in which their rhizomes grow. Many varieties thrive in our region and even more are available as houseplants. While the giant timber bamboos may exceed 100 feet in height, other varieties are only 18 inches tall at maturity. Their cultivation requirements vary somewhat, although typical requirements include sun and ample water. Size and spread can be adjusted to a degree by varying the feeding regimen. There are few pests, although a bamboo mite seems to be looming on the horizon. Containment of rhizomes is usually advised; and “pruning” must sometimes be done with a pick-axe.

We may think of bamboo as native to China and Japan, but there once were enormous stands of it in the southeastern part of the North American continent. While our native varieties are long gone, bamboo is extensively cultivated in many parts of Asia. It is an important food crop—yes, bamboo shoots are simply the interior of the emerging culms—and widely used for building construction and the manufacture of furniture and household objects, both practical and decorative. It is also the largest source in Asia of pulp for paper. Bamboo is revered by many as a sensible, sustainable resource. Its rate of growth can sometimes be measured in tens of feet in just a few weeks.

Stop by the office and take a look at the digital photo of Phyllostachys flexuosa in bloom. If your appetite is whetted for more information about this giant grass, check out the fine book on grasses from the Master Gardener library. There are many other bamboo-specific books and articles available in libraries and on the Internet. I particularly enjoyed my visit to the website of the American Bamboo Society (http://www.bamboo.org/abs/). In addition to links to other sites, there is a wealth of information provided by members. Take a moment to read “How to be with Bamboo,” by Milo G. Clark. It captures the charm of bamboo and the devotion of the bamboo people which is—really!—the term that bamboo aficionados use to describe themselves.