Akadama absorbs water and releases it. Lava rock adds space. What does pumice do that the other two don't do?

From this very website, Bonsai Empire:
"Pumice is a soft volcanic product, which can absorb water and nutrients quite well. When used in a Bonsai soil mix, it helps to retain water and it aids the roots to ramify very well. ... Roots can't grow into Lava rock. Organic potting compost includes peat moss, perlite and sand."

I thought I looked there. Oh, well. Thx.

If the job of akadama is to hold water, and the job of pumice is to hold water, why use both? Why not use lots of one instead of some of both?

Akadama holds more water, and promotes fine roots because small roots are able to penetrate the akadama particles. The downside of akadama is that it breaks down and becomes soggy over a period of 2-4 years. Pumice on the other hand is not degradeable and therefore provides structure and water retention.

Akadama is essential in bonsai cultivation, because of the promotion of fine roots which is essential if you want to promote fine ramification. Without and healthy rootball with many many fine roots - a fine ramification cannot be achieved.

Leung wrote: Akadama is essential in bonsai cultivation, because of the promotion of fine roots which is essential if you want to promote fine ramification. Without and healthy rootball with many many fine roots - a fine ramification cannot be achieved.

Now why do you think this? It is of course not true. As an example, look at the bonsai by Harrington. He does not use akadama.

Leatherback - actually it is very true, that being said, I did not mention that it cannot be substituted with something else.

Taken from the web:
About Akadama and Kanuma

Akadama and Kanuma have been used for centuries in Japan. This is one of the reasons you see such beautiful bonsai in Japan. The bonsai masters use these soils, which are a type of pumice only found in Japan, especially for their prized specimen bonsai.

There are many reasons why akadama and kanuma are used. They both retain the right amount of moisture, nutrients and air for a healthy and thriving bonsai. Both promote fine feeder root development because of the special nature of the soft pumice they are. Trees only need less than one third of their root system for growth and nutrient uptake, the balance is used to secure them in the soil so that the winds will not blow them over. In bonsai, you only need the fine feeder roots actually. Most Western derived bonsai soils do not promote the fine fibrous feeder root system that akadama and kanuma do.

You control the amount of fertilizer and nutrients to keep your bonsai in the best condition possible.

Once you have used akadama and kanuma, you will understand why it is used in the highest quality bonsai in Japan. They promote healthy vigorous growth and when it comes to re-potting you will notice the fibrous root system and ease of removal of the soil from the roots.

Leung wrote: Leatherback - actually it is very true, that being said, I did not mention that it cannot be substituted with something else.

Actually, you said just that. you said it is essential. Which is exactly what I meant with it is not true.

Yes akadama works for some people under the right climate (In my climate you will have to repot every 2-3 years. Else you only have mud. ). But it does not work everywhere. And you can get the same results with other substrates.

Actually your are quoting me out of context. If you look at the subject and what the original poster was asking about - then I think my answer is quite right.

I've been using akadama in my mix for most of my plants, the type known as "hard akadama".
I like it so far, but I never tried it as the only component, it's always a percentage of the mix.