Bonsai: correcting trunk taper

Trunk taper is a core part of good standard bonsai design. The golden rule of triangles almost depends on this being balanced with a good branch structure. Unfortunately not all trees are fit for purpose with some trunks being as thin as a whip and others thick as a log. Others undulate with some parts of the trunk thicker than others.

Each of these presents its own challenges and benefits that need to be addressed

A tree trunk that is too thin can be easily overcome given enough time and planning.

A trunk that is too thick needs to have the energy for growth redirected or to have the branches developed

A trunk that has reverse taper is the most challenging. You can embrace it fully with a very atypical design or you can try to correct it. Correcting reverse taper is hard.

Other than time, feeding and growth a tree can be grafted in a number of ways to create or at least enable growth of the trunk. You can graft new roots or even a whole sapling to the trunk. Extreme and brutish but effective means of achieving growth.

Relevant links:

Inarch Graft Technique – How To Do Inarch Grafting On Plants
https://www.gardeningknowhow.com/gard...