When to harvest bamboo? Wet or dry season?

[Scott]

Generally I had read that bamboo to be used for construction should be harvested in the dry season, as the starch content was lower.

Although I few times I had read the opposite, that the wet season is better. Recently I got 'Bamboo: Gift of the Gods" and it says to harvest in the wet season, so now I'm really confused.

This is an important issue, as it affects the life of the bamboo. Can anyone offer input? I was wondering if it had to do with different climates or varieties of bamboos.

I'm living in tropical Thailand, in the northern hemisphere, in case that matters.

[humanitarianbamboo]

In response to when to harvest bamboo

From all the research i have undertaken to date
it appears the right time to harvest bamboo is when sap levels are at their lowest, as this means their are less sugars in the bamboo making it less attractive to pest infestation once harvested. This effect may be ameliorated to some effect by a range of methods of water leaching or through encouraging ongoing photosynthesis after harvest.

Their are a number of cycles that impact the harvest time

1) The life cycle of the plant
Bamboo grows to full height and growth in a single rainy season
over the next year it matures, sprouting branches during the second year and beginning to harden and toughen. By the third year the wall of the culm has firmed up and is taught an strong, ready to be picked. Over the next years mould and fungus begin to attack the plant, which unlike timber has not produced toxins to protect itself, so that b y the 5th to 7th year depending on the species the bamboo is too old and too damaged to be of much use
Hence in life cycle terms the plant should be picked between its 3rd and 5th-7th year depending on species

As a minor note, by the 5th to 7th year a newly planted culm has reached a stage where their is sufficent growth of both new and old culms to support a full harvesting capacity.

2) The 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 rain fall period sap levels are at their highest, with sap levels diminishing towards the dry season. Picking immedietly prior to the wet/growth season may also damage new shoots.
Hence harvesting is best at the end of the dry season, a few months prior to the start of the wet
(in Thailand this will vary from the north to the south but will mean harvesting around october november december january)

3) Moon cycle
As the moon travels around the earth it goes in and out of alignment with the sun. When in alignment either in a full or a new moon, the gravitational pull at the equator is much stronger, distorting the shape of the planet and it's tides, producing higher sap levels in plants.
This means that the best time to harvest is on a waxing or waning moon.
(please note that this may vary from species to species and local traditional bamboo using communities will almost certainly know the best time for that species)

4) Daily cycle
During the peak of the day photosynthesis is at it's peak producing the highest levels of sugar in sap, making this the least ideal time of day to harvest.
Many traditional practitioners believe that the best time to harvest is at dawn or dusk on a full moon. This practic makes sense in terms of both moon cycles, visibility and daily cycles.

Removal of SAP post harvest
In many areas of the world the sap levels in harvested bamboo are reduced either through leaching of photosynthesis.
Examples of this practice include:
a) Cut bamboo is raised clear of the ground and leant against the rest of the clump for 1 -2 weeks until leaves turn yellow to allow full consumtion of sugars by the plant
b) 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
c) Cut culms are immersed in a running stream and weighted down for 3-4 weeks (in thailand famously bamboo from the norther mountains were tied together and slowly floated down to the capital over 3-4 weeks for use in the city)
c) 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)

When using water leaching, it should be remembered that slow even drying in the shade, will reduce cracking in the outer skin of the bamboo, hence reducing opportunities for pest infestation.

It should also be remembered that 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 in a better designed structure

Please see attached gif for a clearer explanation of the tidal effect