The art of bonsai is full of magic. Creating a bonsai tree masterpiece does take time, patience, dedication, as well as following the basic principles of the ancient practice involving the Japanese tradition and aesthetics.

However, there is also a big room for experimenting and further adding your personal touch to bring out the exquisite beauty of your bonsai while leaving a part of your soul on display.

Working with the trunk of a bonsai tree is one of the most important steps of your miniature trees cultivation journey. Let’s find out how to split a bonsai trunk with best results upon completion.

What is the Function of Bonsai Trees’ Trunks?

Japanese Bonsai artist Tomomi MoriImage Source

Before you get down to actually splitting the trunk of a bonsai tree, you need to understand the function of trunks.

Above all, the trunk of a bonsai tree and the trunk of any other regular tree does serve the same vital functions.

Firstly, a trunk is what supports the entire tree. When the forces of nature affect a tree, it is the trunk that “absorbs” the effects of these forces. In fact, the more external forces affect a trunk, the stronger it grows.

When it comes to bonsai trees’ trunks, allowing external forces and/or intentionally applying techniques that mimic the effects of external forces in nature, are ways to achieve the captivating, aged appearance that is highly treasured in the art of bonsai.

Apart from supporting the tree, it is through the trunk that essential nutrients, as well as water, are transported all the way up to the hungry leaves and/or flowers.

What’s more, it is through the trunk that carbohydrates produced in the leaves can travel all the way down to the roots.

Video by: Lovely Trees and Gardens – Plant ID: Tree Trunk Anatomy

Bonsai Trunk Thickening Techniques

Example of bark splitting technique for creating a solid NebariImage Source

As a rule of thumb, an exceptional bonsai tree trunk starts with a good, strong Nebari.

Nebari refers to the root flare that is further intertwined with achieving the gentle thinning of the trunk towards the highest point.

It is also essential that the thickness of the trunk is dominant, as compared with the thickness of the leaves so that the tree can look as authentic as possible.

Keeping in mind that the trunk is the very base of a bonsai tree, it is a crucial part of the whimsical visual appeal of a miniature masterpiece. However, achieving the desired looks is not deprived of exciting challenges.

Many bonsai tree gardeners – no matter of their level of experience – can be faced with weak and/or narrow trunks. But on the bright side, there are numerous techniques that can be applied in order to achieve a thicker, fuller trunk.

First off, gardeners can choose to encourage the growth of a sacrifice branch.

The sacrifice branch technique takes advantage of the way branches can be used to direct nutrients to the tree trunk before they are cut off once the desired thickness is achieved. Sacrifice branches do not add to the bonsai trees’ appeal, that’s why careful planning can help to direct their energy to thicken the trunk before removing them.

Secondly, transplanting a bonsai tree outdoors can be truly helpful in thickening the trunk.

When growing outdoors, a bonsai tree’s root system has the chance to spread wider and deeper, allowing for the gradual thickening of the trunk. However, planting a bonsai tree outdoors is not always an option, especially for urban bonsai enthusiasts.

Thirdly, you can keep cutting back the trunk, starting at a spot where the trunk has already reached the desired thickness.

The idea is to let new branches/leaders to grow, thus, creating a new section. When the new section gradually gets as thick as you want it to, the process is repeated over and over again. This particular technique can take years to reach the desired appearance of a thick, full trunk. In fact, it can also become curved and even more stunning.

Splitting a Bonsai Trunk: Step-by-Step

Finally, you can learn how to split a bonsai trunk in order to achieve an almost immediate, as well as a long-term visual difference of a trunk’s thickness. Indeed, the trunk splitting technique is the fastest of all the methods we discussed so far.

Step 1: Brush soil from the roots

You need to remove your bonsai tree from its container and make sure all the soil is brushed away from the roots.

Step 2: Split the trunk to the middle

Now, you need to hold your bonsai tree upside down. Using a saw or rotary tool, carefully split the trunk to the middle. Aim for splitting it up about midway but not any higher.

Step 3: Re-pot the tree and help it heal

Once done splitting the trunk, it’s time to re-pot your miniature tree. It’s a must to help it heal faster by taking advantage of wooded wedges or wire. The idea is to make sure that the two sections of the trunk are held apart.

Keep in mind that even though this method is the quickest one, it still takes years before the trunk is fully healed.

Video by Bonsai Iligan – Bonsai Experiment: Creating Nebari with Split Bark Technique

The Wrap-Up

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Quintessentially, working a bonsai trunk can be a process full of excitement and joy. However, it is also a must to do your research and planning properly, or else, the methods you choose to apply may do more harm than good.

Anyone can learn how to split a bonsai trunk – it’s a fairly simple task. But don’t forget that the process is traumatic to your tree. Being a form of injury, splitting a bonsai trunk should only be applied to vigorous, healthy plants. Ficus, Juniper, Boxwood and Elm tree species are among the ones that tolerate this particular technique best.