Why trunks grow thick
When developing a plant for bonsai we want to grow a trunk with taper that radiates the feeling of age and resistance to the forces of time. To do this is is important to understand the basic fysiology of plants, and how a trunk is formed. In a few short sections below, an explanation of why trunks get thicker, how to speed up the thickening process and why plants in a bonsai dish never develop a thicker trunk.
Why do trunks grow?
Between the bark and the inner wood in the tree we found a layer of cells called the cambium. This layer of cells is the only layer that is actually causing growth. When the plant is active, the cells in this layer divide and creates new tissue on both sides of the cambium. On the outside, the cells become part of the bark, and become part of the phloem. On the inside, the cells become part of the Xylem. This dividing of cells create the increment of trunk thickness. Importnat to note is that the growth of the cambium is directly related to the growth of the sap-transport through the bark and sapwood.
How to increase trunk growth
Because the growth of the trunk is directly related to the transport of sap through the bark and sapwood, it is important to maximize sap transport. The way to do this, is by increasing the above-ground biomass, in other words, the number of leaves and branches. In order to provide the plant with enough water and nutrients to sustain massive growth, naturally the roots need lots of space to grow. This means your roots will also have a strong growth, affecting the nebari. This in intself is not a big problem: A strong trunk with character requires a strong rootbase in order to balance the total image. So besides growing a trunk, you are also working on a strong nebari.
Naturally, in order to grow the best possible trunk for bonsai, a trunk should not just be thick. It also should have taper and character. In order to learn how to do this, How to do this, continue reading Growing bonsai trunks.