Although a few species of bamboo are always in flower at any given time, growing a specific bamboo typically requires obtaining plants as divisions of already-growing plants, rather than waiting for seeds to be produced.
Timber is harvested from both cultivated and wild stands, and some of the larger bamboos, particularly species in the genus Phyllostachys, are known as “timber bamboos”.
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Bamboo used for construction purposes must be harvested when the culms reach their greatest strength and when sugar levels in the sap are at their lowest, as high sugar content increases the ease and rate of pest infestation. As compared to forest trees, bamboo species grow fast. Bamboo plantations can be readily harvested for a shorter period than tree plantations.
Harvesting of bamboo is typically undertaken according to these cycles:
1) Lifecycle of the culm: As each individual culm goes through a 5– to 7-year lifecycle, culms are ideally allowed to reach this level of maturity prior to full capacity harvesting. The clearing out or thinning of culms, particularly older decaying culms, helps to ensure adequate light and resources for new growth. Well-maintained clumps may have a productivity three to four times that of an unharvested wild clump. Consistent with the lifecycle described above, bamboo is harvested from two to three years through to five to seven years, depending on the species.
2) Annual cycle: As all growth of new bamboo occurs during the wet season, disturbing the clump during this phase will potentially damage the upcoming crop. Also during this high-rainfall period, sap levels are at their highest, and then diminish towards the dry season. Picking immediately prior to the wet/growth season may also damage new shoots. Hence, harvesting is best a few months prior to the start of the wet season.
3) Daily cycle: During the height of the day, photosynthesis is at its peak, producing the highest levels of sugar in sap, making this the least ideal time of day to harvest. Many traditional practitioners believe the best time to harvest is at dawn or dusk on a waning moon.
Leaching is the removal of sap after harvest. In many areas of the world, the sap levels in harvested bamboo are reduced either through leaching or postharvest photosynthesis. Examples of this practice include:
Cut bamboo is raised clear of the ground and leaned against the rest of the clump for one to two weeks until leaves turn yellow to allow full consumption of sugars by the plant.
A similar method is undertaken, but with the base of the culm standing in fresh water, either in a large drum or stream to leach out sap.
Cut culms are immersed in a running stream and weighted down for three to four weeks.
Water is pumped through the freshly cut culms, forcing out the sap (this method is often used in conjunction with the injection of some form of treatment).
In the process of water leaching, the bamboo is dried slowly and evenly in the shade to avoid cracking in the outer skin of the bamboo, thereby reducing opportunities for pest infestation.
Durability of bamboo in construction is directly related to how well it is handled from the moment of planting through harvesting, transportation, storage, design, construction, and maintenance. Bamboo harvested at the correct time of year and then exposed to ground contact or rain will break down just as quickly as incorrectly harvested material.
Maintenance of spreading runners
Regular observations at ground level indicate major growth directions and locations of rhizomes. In dry and hard soil conditions extending rhizomes will cause cracks in the soil surface. To facilitate rhizome maintenance it’s best to dig a furrow around the bamboo planting and/or plant in a raised mound or bottomless lumber frame box. During “root pruning” of running bamboo the cut rhizomes are typically removed; however, rhizomes take a number of months to mature, and an immature, severed rhizome usually ceases growing if left in-ground. If any bamboo shoots come up outside of the bamboo area afterwards, their presence indicates the precise location of the removed rhizome. The fibrous roots that radiate from the rhizomes do not produce more bamboo.
Bamboo growth can be somewhat controlled by surrounding the plant or grove with a physical barrier. Typically, steel, concrete, and specially rolled HDPE plastic are used to create the barrier, which is placed in a 60– to 90-cm-deep ditch around the planting and angled out at the top to direct the rhizomes to the surface; this is only possible if the barrier is installed in a straight line. Regardless of size of area, blocking bamboo rhizomes as a solution to controlling running bamboo is detrimental to the health of the plant, and only temporary. Bamboo within barriers usually become rootbound after a few years and start to display the signs of any unhealthy containerized plant. In addition, rhizomes pile up against the barrier and often escape over the top or under the bottom. Strong rhizomes and tools can penetrate plastic easily, so care must be taken. In small areas, regular root pruning maintenance may be the best method for controlling the running bamboos. Barriers and edging are unnecessary for clump-forming bamboos, although these may eventually need to have portions removed if they become too large.
The ornamental plant marketed as “lucky bamboo” is an entirely unrelated plant, Dracaena sanderiana. It is a resilient member of the lily family that grows in the dark, tropical rainforests of Southeast Asia and Africa. “Lucky bamboo” has long been associated with the Eastern practice of feng shui. Images of the plant widely available on the Web are often used to depict bamboo.
Phyllostachys species of bamboo are also considered invasive and illegal to sell or propagate in some areas of the US. On a related note, Japanese knotweed is sometimes mistaken for a bamboo, but it grows wild and is considered an invasive species.