Bonsai Growth Media
Soil mixtures vary a great deal depending on geographical area and personal preferences. There are many conflicting ideas on the type of mix to use.
Many growers find that bagged potting soil is satisfactory for potting bonsai plants. If you use bagged soils, make sure they contain sphagnum peat moss and coarse perlite in equal quantities. Bagged soils are available in most garden supply houses.
Generally, mixing soil should have rapid drainage, a structure that permits fine roots to develop, and contains decaying humus and mineral nutrients. It should also be free of root rot and have a pH similar to the tree's native soil. Try to avoid high levels of dry fertilizers in the soil mix. Screen bagged soil to remove the fine clay particles.
A good basic mixture consists of one-third clay, one-third humus, and one-third sand. If you live in an area where humus is not available, then obtaining an artificial soil mix from your garden store or nursery is the only answer. River or quarry sand can be purchased from lumber yards and variety stores where it is sold under the name of white aquarium sand.