No matter how much care a tree is given, it won’t survive unless it has the right amount of moisture and good drainage. In the care of bonsai these two factors are of paramount importance.
Basic Mix for Bonsai my husband likes to use contains 1/3 sand (you may find it at lumber yards or at stores, with the name of white aquarium sand) 1/3 peat moss (you can find it at any Home Depot) which increases the air and moisture holding capacity of the soil, and 1/3 soil.
This mix can even be used for any container plant inside your house or outside. The mix won’t compact or hold much water.