Bonsai soils are very different from other potting soils that we might use in our garden or with our house plants because the bonsai is really a living tree that we keep prude and in a miniature form, we have to make some accommodations to the tree to stay healthy in that confined environment. What I have here is an example of the soil, and you can see that it is very lose and gravely and especially formulated for growing bonsai. It is important that, if you have a bonsai tree and some of the soil washes out during watering or you lose some of the soil, that you do your best to try and purchase some regular bonsai soil to replace it with and not replace it with potting soil. Potting soil can do a lot of harm to your bonsai tree. A very important reason for this loose and airy soil, this very gravely soil, is that the excess water must drain each time you water the bonsai tree. Every bonsai pot has a hole in the bottom, at least one hole, and that makes way for the excess water to drain out. If the tree stands in water it will become water logged and it will die quite soon after that.