Bonsai soil...?

First I have to say please excuse my English as it isn't my first language. I hope I make myself sort of clear enough to get my point over...
Soil is the most important part of bonsai. I see so many different combinations and almost all of them contain a certain amount of organic compost or matter. Bacterial critters need that to their work so the plant can take up the nutrients. My problem is there is so many variants (heat, cold, dry, wet, being flushed out etc. etc.) in a container (especially a small one like a bonsai pot) that the critters I think, finds it hard to get established and multiply sufficiently. I really cant see the advantage of trying to grow "organically". Surely the way to go is completely inorganic...?

Quite a few people do go entirely organic.

But there are other reasons to have organic material in your soil mix. It helps to maintain pH on the acidic side, and most inorganic mixes tend toward the alkaline. It also helps hold moisture in dry climates. It also helps hang on to nutrients when you fertilize.

It's late at night here (for me, at least) and I've probably missed reasons. Others can chip in.

Moved to Bonsai Questions.

fredman1,

I have found that the simplest mix is just, inorganic that holds water in itself, inorganic that does not hold water, save around itself, and a blended compost, as the organic.
Particle shape might be better as rounded for the inorganic.

I live in a climate that goes dry for almost six months and then goes wet [ 153 cm on the average for 6 months ] so I can start with a 1/3 or less organic ------------- to 2/3 or more inorganic mix.

You should be able to mix something that works well for you. Plus you have active clubs on your side who can advise you.
Later.
Khaimraj

The purpose of organic elements in your soil is many-fold. First, and foremost, organic elements have a high CEC (cation exchange capacity), as compared to inorganic elements. CEC, in plain terms, is the ability to take up nutrients and release them as the plant needs them. Organic components such as small orchid growers' bark (1/8 - 3/8"), coconut husk (small size) and hemlock and pine bark mulches have a very high CEC compared to the other inorganic elements in your soil. (Note, however, that all of the organic elements mentioned above are granular and drain very well.) Second, organic components in your soil do indeed help with maintaining a slightly acidic Ph. Third, they do provide a good host for beneficial organisms such as Micchorhizal fungi and good bacteria strains.

So, to get to the point, organic soil components (such as those listed above) serve several purposes in bonsai culture...Perhaps the most important of which is being able to absorb and release nutrients (CEC). However, when choosing organic components for your soil, be sure that they drain well. Personally, I find that everything from Japanese Maples to Natal Plumbs, from Black Pines to figs, from Scheflerra to Spruce will grow quite well in the following mix:

1/3 Crushed Lava Rock (Beam Clay*tm size 1/4")
1/3 Turface*tm
1/3 Small Sized coconut husk (1/8 - 3/8"), or 1/3 small orchid growers bark (1/8 - 3/8").

The only exception to this rule (or so I've found) is members of the Rhodo family. In this case, use either straight Kanuma, or the above mix at 50%, and kanuma at 50%.

****All components should be double screened!

As much as anything, I think the choice of soil should be determined by your climate/weather/growing conditions and your own horticultural practices. I know that some very successful grower here in Florida use only Turface, a baked clay product.

Thanks to everybody's responses.  Maybe I did not make myself clear enough. I do have a good mix that I am happy with. I use 1-1-1 screened composted pine bark, granite grit and pumice (all the same size screened)
The thing that bothers me is purely around biological activity in the mix. Firstly there isn't much organic matter in the mix so how can there be enough biological activity? Secondly because of all the environmental variants it cant be a happy place for the biological critters to try and make a decent living inside a small little pot....! In the ground everything is stable and they can multiply and do their work much easier. It does not make sense to me to feed organic fertilizer in a small pot either...
(Hope I make better sense)

Fredman1,

if you need dates for proof, note that I have been using a blended compost [ that has micronutrients ] since the early 80's and I grow mame' [ under 7.5 cm ] never had any problems. In fact working with Yvonne's soil ideas for Ficus, I have improved my growing, by using less organic material.

You should have no problems.
Later.
Khaimraj