In the older days Indians added charcoal to the soil when growing their plants. The result was healthy and vigorously growing plants. Today’s science has shown why charcoal is beneficial for the health of the root system and the plants. What does charcoal do then? It is pretty simple; first of all it takes up nutrients and slowly releases them to the soil. This slows down the process of washing out nitrogen gasses that is useful for the growth and vitality of plants and trees. For container grown plants it is even more useful than for plants in the field, because the nutrients are washed out faster, and therefore charcoal is an important ingredient to add to the soil mixture.
In Japanese bonsai nurseries this trick is widely used, and charcoal should be a natural component of the soil mixture in all bonsai. An amount of five to ten percent of the soil mixture should do the job in most cases. Use a clean natural charcoal and not the briquettes that often are added chemicals.
Break down larger pieces to smaller, adjusting them to the size of pots and trees. In general avoid larger pieces. Mix the charcoal evenly into the normal soil used on top of the bottom drainage layer only. Here the roots will benefit from the slow release of nutrients and nitrogen. Afterwards fill up with normal finer soil at the sides when the tree is securely fastened in the pot as usual procedure.
It doesn’t matter if you use Akadama or other soil mixtures. The charcoal is widely used in all types of soils and the effect is the same.
My advice is that you should pick up locally available soils to avoid unnecessary transport of soils across the world. Many wants to use Akadama, but no need for that if you have a good soil available locally. Akadama has a great function as soil in warmer climates, where the clay holds water for a longer time. Here in Northern Europe with a cooler climate, it is necessary that the soil doesn’t stay wet too long. So another type of soil is needed, without clay involved that also breaks down and become very compact when freezing during winter time.
High quality soils are sold at much lower costs than Akadama (especially saving the transport costs) at local nurseries and garden centres many places in Europe. In Denmark we have high quality soils used for garden containers that easily replaces the much more expensive Akadama, and works better with the weather conditions here. Added leca pellets (hard burned clay that doesn’t break down) to add air and drainage (or you can use any kind of finer grid), and charcoal for the health of the super small eco system in the pot, this is a great soil mixture for the climate I live in. Charcoal can be added to any type of soil mix, just be sure to have smaller pieces for smaller containers.