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.
Akadama and kanuma are used together in bonsai such as pine, juniper, cedars and other acid loving plants. Kanuma is used by itself in Azaleas, which is the reason that most azalea bonsai in Japan are found in the Kanuma region.