What is bonsai soil and why is it used for bonsai?
As noted previously, potted trees do not do well in soil that is always wet. Potting soil and top soil are heavy soils that can remain wet for weeks.
Bonsai soil is a mixture of ingredients which allows the water to drain freely and at the same time, retain moisture. In addition, the ingredients allow the roots to breathe air and prevent compaction.
There are two basic types of bonsai soil -- a conifer mix and a tropical/sub/tropical mix. Before adding any soil mixture, be sure to cover the drainage hole(s) with screening to prevent the soil from washing out of the pot. When re-potting, it is always best to use the soil mixture in its dry state.