I use akadama for all my trees, except the azaleas for which I use kanuma. These work perfectly in the climate here (North London). They both drain very well and both hold suficient water that I am not having to water every hour in summer.
In this climate I need to water once a day in summer. Twice if it gets really hot (in July/August). Because I use the same media, the drying times are consistent between trees (pot size notwithstanding), which makes the need for water predictable and so eliminates any nasty surprises in high summer.
Double line brand akadama is hard enough to hold its integrity for many years. Only the top 0.5 inch breaks down due to freezing and constant wetting/drying. Below half an inch where it stays consistantly damp, it holds its structure and all I need to to is top dress every other year. I have a black pine that's been in the same pot for four years so far and after top dressing this year, still drains like it was just repotted.
Kanuma, because if what it is, tends not to break down anyway.
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Originally Posted by FredL
I see myself trying to create a good soil ecology, not a sterile hydroponic environment. I want my trees to be little pieces of the natural world, not artificial constructs. When I see the term "living sculptures" used to describe bonsai, I see the emphasis as being on "living".
And, that goes for the soil as well.
Fred
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I agree with this completely. It's the nature of nature that (abhoring a vacuum) any initially sterile medium will only be that way for a very short time unless kept in a lab. After watering in a freshly repotted a tree (in akadama or kanuma), the media become inoculated with all the spores and bacteria that the rainwater carries (I only use rainwater), plus what was on the roots of the tree to begin with.
Add a comaratively gentle fertilizer (organic cakes) and mineral suppliments like maxicrop and within a few weeks the pot is a thriving ecosystem of microorganisms; bacteria and beneficiel fungi. I can smell the rich, loamy scent every time I water (I love it). If I scratch away the surface layer of the akadama my pines are in (e.g. when top dressing), I can see the pots are
full of mycorrhyzal hyphae. I can see it at the drainage holes too.
I'm a strong believer in; 'Feed the soil and the tree will look after itself'. I do use chemical feeds to boost trees that are growing on, but mainly as a foliar feed and only rarely as a soil drench (it's a bit harsh on the beneficial fungi and inhibits its growth).
I'm not suggesting pure akadama/kanuma is the best, or even good for everybody, but for my particular circumstances and climate, these two potting media offer the best solution. They give me simplicity, consistancy and predictability (controllability) and give my trees excellent drainage, lots of air and good water retention, plus an ideal ecosystem for all the microorganisms that everything depends on.