Reply To: Organic soil
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I stopped using organic soil for my established bonsai some time ago now as I didn’t find a positive effect adding it.
If you watch the last Live Q&A recorded we deal with it.
Shortly here: Organic soil is cheap and great for growing young material and plants fast where it isn’t an issue that roots grow long. It is actually a good thing that roots grow long and strong because it speeds up growth, and thickens branches and trunks.
Using harder soil types (like Akadama) is great for trees we want to have a dense ramification and slow and compact growth. Akadama divides the roots when they grow into the soil and split. That slows down growth, giving a dense root ball, leading to shorter branches and ramifikation.
Adding a bit of organic soil to the free draining Akadama soil in theory will hold water a bit better. But I have so far not noticed any difference, so I simply stopped doing it anymore.
A bit of moss at the surface during mid-summer to prevent humidity to evaporate too fast, and placing small trees in a shallow water basin does the trick in very hot weather.