Repotting heresy-II

OK, Mirai acolytes, here is something to chew on. As repotting season approaches, I’ve been reading some background material. I came across this article and had some questions about repotting time. The author says that in some trees the vast majority of energy is stored in the roots. If we remove 30-50% of the roots prior to repotting, aren’t we removing 30% of the stored energy? It seems somewhat counterproductive. We bust our humps to make sure we have as much energy as possible for the spring growth and then, right before we use it, take 30% away. The study shows that once shoot extension is finished and all the energy utilized, new roots began to form and energy resupply begins. So, would it be better to repot when shoot extension stops? The roots that are removed won’t needed again and will be replaced by new healthy roots.


I think you are missing a few important parts.

  1. New foliage mass looses a lot of water. So your roots need to be doing their job well in order to meet the higher demand for water.
  2. Once the tree has used all that energy for foliage what will you grow roots with? I imagine the idea of repotting as buds swell is that the tree has started moving resources out of the roots up to the buds, but there is still time for the tree to reallocate some of that energy toward root growth.
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And to take your second point further, I think that if repotting and root reduction is done in the spring, when new buds are swelling, the tree has time to react to the reduce root mass. I would assume that the new growth might be more compact with smaller leaves to compensate for the reduced water uptake capability caused by the root reduction.
And don’t get me wrong, I don’t think this is a viable method to reduce internode length or leaf size, just that it is a by product of the repotting.

A third point in favor of repotting in the spring is that temperatures are a lot lower in the spring than in early summer. If root reduction is done in the spring, the tree has more time to generate new roots before the heat of summer kicks in and the tree needs all the roots it can have to transport enough water to keep the leaves hydrated.

Disclamer: I’m a mere bonsai noob, the thoughts above are only based on my limited understanding of plant physiology learnt by watching the Mirai streams.


The idea is to repot once the energy has been moved towards foliar growth but before the new foliage needs water so as soon as you got that indication from buds swallowing. Like others mentioned, once the foliage is out in the spring, it needs more water and the newly repotted root system may not yet be able to provide it. It also depends on how aggressive is the necessary root work and how well developed the root system is.


Yes, repotting removes some of the stored energy of the tree. We know this procedure is going to cause a setback and might result in a weaker flush of growth. This is part of why Ryan stresses repotting when necessary as opposed to doing it on a schedule. I think a lot of us have been performing the task too frequently instead of thinking about what we are trying to accomplish.


@Micke :+1: Well said! :+1:


Also remember that different species store energy in other parts of the tree. Some store energy in their roots, others it’s in their foliage and then vascular.

@rafi I have heard this Chabasai is a zeolite crystal of some sort. In doing some research it appears to be a viable soil amendment. It reportedly has a really high CEC and does not break down. I also found that it holds water well and releases it slowly. I’ve seen it used as an aquarium filter medium as it soaks up toxins like ammonia. I also read that it stabilizes pH as it buffers against changes due to the absorption and binding of salts. I could not find any specific information about its pH when used as a soil amendment, do you happen to know what it may be?
Thanks for sharing Rafi!

Chabasai has pH 7.0 and CEC of 230 meq/100g A lot of other info (in french) can be found here:

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Thanks good to know! Have you had any health with any acidic-loving species?

I don’t know if any of the species I have are acidic-loving. For one, I don’t have any azaleas.