Akadama is a natural volcanic Japanese clay. It’s a (commercially produced) hard-baked clay that is widely used for bonsai purposes. Akadama is used to improve the drainage of the soil mixture and comes in different grades (from small, to medium and ever larger particle sizes).
Because it’s a hard-baked clay it produces fine grit or dust, which should be sifted out before adding it to any soil mixture. Why? Well, the fine grit can counter the exact purpose that the clay is used for in the first place; drainage.
Akadama has a high C.E.C. and neutral pH value.
Akadama has excellent drainage capabilities and therefore a commonly used component in bonsai soil mixes.
Akadama is not frost proof. In colder climates, the grains will be reduced to very fine grit or dust after one (or more) cold winters. When this occurs, the Akadama will lose all its benefits and will no longer be usefull for bonsai cultivation.