Flowering Bamboo Presents an Opportunity

When a bamboo flowers, as most of us know, it is in danger of dying. Flowering bamboos do not always die; although many do -- especially in the case of gregarious flowering. Even an individual plant that suspends growth of new culms and foliage for the exclusive production of flowers may die.

The phenomenon of gregarious flowering may involve many plants, but not necessarily all plants of that species or clone. Sometimes bamboo of a species growing over a large area may flower at the same time. For those of us cultivating bamboo, we may have many plants that are a single clone or closely related seedlings and there is a danger that all or most of a given type may flower and die. As with all plants, flowering and reproduction from seed is necessary for the survival and
spread of the species. There are bamboos that do not flower and, therefore do not set seed. But these bamboos are not found growing in the wild. They are dependent upon man for their survival. Once mankind finds them of no further value, they will perish.

Since bamboo is anemophilous, wind pollinated, it must have many flowers at anthesis at the same time for successful spread of the pollen. The reason bamboos die after flowering is most likely so that the seedlings will receive the water, nutrients, room and sunshine that would otherwise be used by the mother. The seedlings are mulched by the debris of the dying parent. The mechanism for the timing of flowering and dying is a phenomenon not yet understood. It is one of nature’s baffling mysteries.

What should one do when a bamboo flowers? One option is to do nothing. The plant may recover, or it may die. You could even end up with a multitude of new seedlings at the base of the old plant. Even if it recovers, you will have a mess on your hands. When Otatea accuminata aztecorum flowered at the Huntington Garden near Los Angeles a few years ago, they left the whole dead plant in place. This was quite a bold choice for the gardeners of one of Americas premier gardens. It actually looked quite striking. It seemed to be a ghost of the living plant. Generally dead bamboos look quite dreadful.

One could collect seeds and start a new generation, or could also just remove any dead and dying culms to keep the planting from looking so unattractive. My recommendation is to collect some seed and try growing a new generation under a more controlled environment, and work toward reviving the plant vegetatively. If the plant is flowering on only a few branches or culms, no intervention may be required. However; if the entire plant is flowering then measures are advised. Cutting out flowering culms, fertilizing, and watering heavily have been suggested, but these rarely work. We suggest one of the following.

If the plant is large and in the ground, you should cut off any flowering culms and chop the rhizomes into sections with an ax where they are buried in the ground. This is followed by thorough fertilization and watering and continuing care. We learned this procedure from a Mrs. Lenora Michaels (who lived near Portland, Oregon). She told of doing this when her Phyllostachys bambusoides flowered, and it recovered. It would be interesting to learn how she knew to do this procedure. Many groves of P. vivax and P. bambusoides had been lost during the previous decade, and Phyllostachys bambusoides ‘Castillonis’ disappeared completely throughout the U.S. and Europe. If you have a smaller or potted plant, make divisions of the plant and cut off any flowering culms. Pot up the propagules in good potting soil. If any new culms start to flower remove them also. And of course, you must water and fertilize on a regular basis. Our guess is that this somehow interrupts the flow of some chemical signal allowing some propagules to quit flowering

There has been some research done on the flowering and rejuvenation of bamboo in China. Hsiung et al. (1981) report on experiments with P. vivax, which flowered in Jiangsu and Zhejiang Provinces from 1969 to 1976. Their method for fast rejuvenation was to dig up rhizomes (without culms) from the flowering stands and cut them into 30-50 cm sections. These were dipped in a 100 ppm gibberellic acid solution for 5 hours and then buried in a cutting bed. When new shoots emerged, they were sprayed with the solution every two weeks. After 3 months, 36% of the culms from treated rhizomes flowered, while 64% of the culms from untreated controls flowered. After a year, the treated culms produced more normal, non-flowering culms than the controls. Hsiung warns that “ . . . nitrogen fertilizer does not necessarily stop the flowering of bamboo stands, sometimes it tends to retard their rejuvenation.”

We don’t know which plants we will be able to save. So far our method seems to work with at least some of the Phyllostachys. Some bamboos recover on their own after flowering while others may not recover vegetatively no mater what you do. The latter is more likely if the plant is small or weak at the onset of flowering, although even large and healthy, some bamboos such as Fargesias may flower and die no mater what you do. But like many generalizations, this does not always hold. Phyllostachys elegans at The Bamboo Garden has flowered sporadically every year for about 10 years while continuing to grow with moderate vigor. It, has not been restored to a vegetative, non-flowering state, by our prune and divide strategy. It continues to flower and grow with no sign of stopping. Some species of bamboo seem to have a few plants in flower somewhere most of the time. In China there always seem to be some Moso plants flowering in any given year.

Growing from seed is exciting. It however, is not the way to save a flowering bamboo clone with variegated leaves or yellow or striped culms. These and other special clones are best saved vegetatively if possible. The seedlings will most likely return to the original type. You may though, grow a plant that is more vigorous, hardier, more pest resistant than the parent. Or, perhaps you will discover some other variation from the parent. Perhaps you could even create a bamboo hybrid if you have more than one kind in flower at once. We have had several variegated bamboo seedlings at the Bamboo Garden near Portland Oregon. Some bamboo seed, such as Phyllostachys need to be fully ripened before harvest. This is especially true if the seeds are not to be planted immediately. Seeds of some bamboos are viable and may be planted while still green. Sasas, Indocalamus, and Pleioblastus are in this group. When seeds are very easily removed from the inflorescence they are most likely ripe. Even with these bamboos, it is probably a good idea to let them dry and thoroughly ripen if they aren’t to be planted promptly. Leaving seed on the plant can be chancy though, as birds, bugs and rodents may harvest the seeds. If possible you may want to protect the plant. The seeds even may fall as the result of wind or just bumping the plant.

Seeds may be harvested individually by hand on a small plant. Or sometimes seeds are found on the ground under the plant. If possible you can place a tarpaulin beside or under the plant and shake the flowering culms over the tarp. If you are sure the seeds are ripe, you can cut the culms to make it easier to shake them on the tarp. After collecting the seed and probably much chaff and debris, you can use the wind or a fan to blow away much of this waste.

Formerly, I used to place the seed directly in small pots which I then watered and placed in plastic bags until the seedlings had grown a few inches. Now, especially if I have only a few seed, put the seed between moist paper towels which are placed in plastic bags in a warm place until germination. Then, I put them in the small pots which I also put in plastic bags. A good soil-less mix, good watering techniques, and bright (not direct sun) light, are important to grow bamboo from seed.

Two of our recent projects are the recovery of Phyllostachys flexuosa and the attempt of the recovery of Phyllostachys aurea albo-variegata. As you may surmise by the preceding statement, one project is working and the other is still in question. We have had success with the Phyllostachys flexuosa recovery.

When the P. flexuosa flowered in the ground at our nursery, we dug several plants, cut off all the culms, and divided them into small propagules, and potted them in small pots. Much of the new growth flowered as had the original culms. So we removed any culms that flowered. But, by this time they had many healthy leaves and had given the rhizome a small increase in energy so that they were able to put up more small culms. Most of these new culms did not flower. Not all plants have recovered. Some plants were not carefully attended too, and died. Others though continue to flower. We also collected seeds and are growing a new generation of seedlings. There is new growth in the grove also, but this growth is where we cut the flowering culms so that we could easily harvest the seed. The new culms are very slender and some of them have started to flower. The plants in the grove might also recover, especially since we have cut out most of the flowering culms. And, of course they may have recovered on their own. Some other plantings of P. flexuosa in Europe and California have died. The Phyllostachys aurea albovariegata is quite a different story. Last fall we dug some plants of Phyllostachys aurea albovariegata from a field near Eugene Oregon. We first collected all of the seed that we could, by cutting the culms and shaking them over a tarp. We dug only a couple of plants and left several in the field intending to dig them later.

I digress, vegetative recovery is what we wish to achieve when we are working with a special clone such as this. Our success has not been so clear, or perhaps we have hardly any success as of yet. The plants we brought back to the nursery, we divided sharply as we have suggested in the article we wrote with Dr. Richard Haubrich. These plants have not fared so well as those of the P. flexuosa. On a few small plants we have removed any culms that are not fully variegated. The culms on these are very small and spindly. Hopefully at least one will survive. Just cutting off the flowers did not seem to work. They continued to flower. Complete removal of flowering culms forces the plant to put up new culms. This worked, but any culms with variegated leaves flowered. New culms with no variegation did not flower. Some culms were partly variegated, and on these only the variegated parts flowered. It seems that we may loose the variegated Phyllostachys aurea. The plants left in the field were cut way back, and hopefully this will stimulate new growth in them. We have not been able to return to check on them.

We also have grown seedlings of the Phyllostachys aurea albovariegata, and a few of them showed a little variegation at first. But it has disappeared. We have marked these plants to watch closely to see if the variegation reappears. We have also noticed a very interesting growth pattern which we are also watching with interest. Some of the seedlings are very compact with the leaf sheathes overlapping one another quite closely while others growing in the same conditions are long and lanky. We wonder if perhaps those that are very compact may be the ones to even more strongly show the tortoiseshell, or Buddha belly form that has inspired the Japanese name Hotei chiku (fairy land bamboo). Or perhaps, the taller ones may grow to be like the variety ’takemurai', without the congested internodes of the type species. Whatever the results it is exciting to speculate on the promise of the new seedlings.

Even with attempted vegetative recovery attempts, new varieties can occur. According to Dr. Richard Haubrich, the highly variegated Phyllostachys bambusoides we donated for the auction at the annual ABS meeting at Quail Gardens in October 1996 was found at the base of a flowered out Phyllostachys bambusoides castillonis. I feel that for so highly variegated plant to survive it must have been a sport rather than a seedling. The original Phyllostachys bambusoides Kawadana, was found on a recovering, flowering regular Phyllostachys bambusoides The plant we now have as Phyllostachys bambusoides Kawadana Mike Bell saved as a sport from a flowering Phyllostachys bambusoides castillonis in Cornwall England. So, don t just let your flowering bamboos perish, save them and perhaps, grow something new.

Action to attempt vegetative recovery of a flowering bamboo should be initiated promptly since some bamboos die quickly after the onset of flowering. Some die in less than one year. The bamboos that flower and die so quickly may be beyond our ability to affect any procedure to
revive vegetatively.