Up until yesterday, I believed that all bamboos are hollow. Turns out, it`s not true.
Let`s look at some basic facts about bamboo.
Bamboo is a perennial evergreen plant. It is a part of the grass family even though many bamboos are quite woody.
An important characteristic of a bamboo plant is a jointed stem which is called a culm. The interesting part – typically the culms are hollow but some species of bamboo have solid culms.
Bamboo segments (internodes) are usually hollow inside and form bamboo cavities. Depending on the bamboo species, the wall thickness of the stem can vary greatly from thin walled to even solid.
Each internode begins and ends with a solid joint called a node. Nodes not only divide the segments of bamboo culm but also are the spot from which the leaves and branches grow.
Similar to the culms, the branches are also segmented with nodes and internodes.
How filled or hollow culms are, varies from one bamboo to another. However, bamboo culms are broadly classified as solid or hollow if compared by the internode types.
Solid culm bamboo
Solid culm bamboo plants have thick walls with visible nodes. They are more prone to bending than being straight.
These bamboos can be nailed without them splitting. And even if splitting does occur, the marks are usually externally invisible. They are also rot resistant.
Because of those characteristics, solid culm bamboos are mostly used in the construction and furniture making industries.
Hollow culm bamboo
Hollow culm bamoos are straight structurally and have less visible nodes. They are easy to treat and shape.
Poles made out of hollow culm bamboo plants are prone to splitting. They will also rot if exposed to high levels of moisture.
They are highly flammable because of the hollow internodes.
What this means for practical use of bamboo
The number of solid culm bamboo species is way lower than the hollow ones. It`s safe to say most bamboos are hollow.
We can look at this fact and think of it in practical terms. What does this mean for our use of bamboo?
From a mechanical stability point of view, a hollow stem is much more rigid and stable than a solid (but much thinner) stem composed of the same amount of biomass.
That means the hollow stems of bamboo are very useful and efficient construction material.
It is not to say that it would be better for bamboo to be completely a completely hollow cylinder. The solid node discs in culms are really important for increasing overall stability and ability of culms to resist deformations.
Because bamboo is a strong and efficient material it is often used as a construction material in places where it`s native. Which is not a surprise.
But that is not the only way the hollow culms prove to be useful for people.
In many Asian cultures, the empty hollow in the culms of larger bamboo types is often used to cook food.
Tea is another food-related thing that can be made with the help of bamboo – it is sometimes rammed into bamboo hollows to produce compressed forms of Pu-erh tea.