Developmental soils - Different root type, different growth?

Hi everyone,

Something for discussion…

It has been my understanding that, when developing bonsai, we use a more organic-based soil (like a pumice/composted pine bark mix) to maximise growth (assuming we are unable to grow in the ground). and the reason we do this is to develop a coarser root system, which will be reflected in coarser growth of trunk and branches, before transferring to aggregate substrates in order to refine our trees (the assumption being that these aggregate bonsai soils will produce a finer root system which will similarly translate to finer growth of branches).

However i can’t find any literature that supports the notion that the root and foliar characteristics are mirrors of one another. I have been involved in a number of discussions which refute this hypothesis on the basis that:

“It is the fine roots that take up water and nutrition. Therefore, the more fine roots there are, the greater the amount of water and nutrition that can be utilised, and the greater the amount of growth”

My background is in medicine so can tell you how the human body works but am very much a beginner when it comes to plant physiology. But i do like to support my knowledge with evidence so i was wondering if anyone could shed some light on this and had any reading sources that support or refute the idea that root and foliar growth are related so closely.

Many thanks all and happy bonsai’ing!


Look into the scientific literature around the roll of Auxins and Cytokinins in the branches and roots, and the primary sites that those hormones are synthesised by the plant.

Ah, here you go Follow up to the recent Asymmetry podcast on Soil Science with Ian Hunter - #24 by darren

I believe that the other reason to use the organic component in the developmental soil is that it has a really high Cation Exchange Coefficient (CEC) so it will grab nutrients and make them readily available to the plant. Commercial nurseries use a nearly 100% bark mix for this reason (plus it is often low cost). I like to use a 50/50 mix with pumice since that seems to give most of the growth benefits from the bark, but also result in a root mass that is easier loosen up for develop an aesthetically pleasing root structure.

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