This section explains one of the most critical elements. We will detail the characteristics and roles of four basic soil types: mountain sand,　akadama soil, Kiryu sand, and bamboo charcoal. We will introduce suitable mixing ratios for coniferous and deciduous bonsai, along with the reasons for these choices. Additionally, we will discuss the features of mountain sand and how to select soil based on the repotting cycle of different species. This practical knowledge will be conveyed in an easy-to-understand manner.