Very important and to be adapted according to the species...
Bonsai live in pots, which fill up quickly with roots. Therefore, in order for the roots to live well, bonsai are grown in various substrates in the form of grains. In this way, they have enough space between the grains of soil for air to enter. This is necessary for the roots of the bonsai to breathe without difficulty. But as we have already said, this influences the frequency of watering. As a solution to this problem, we find many bonsai species grown in substrates that retain more or less water. Thanks to this type of substrate, beginners have less difficulties in terms of watering frequency.
Below, a part of the substrates.