Bonsai styled from woody plant material need good natural air circulation and the natural outdoor humidiy. Remember to maintain your bonsai as you would your landscape trees. Keep the bonsai which require partial shade in partial shade. The criteria for bonsai soil mixes is that they should be quick draining, have a structure which permits fine root development, contain decaying humus and mineral nutrients. Soil mixtures vary a great deal depending on the local availability of products and personal preferences.
Many growers find commercially bagged potting mixes satisfactory.
You can substitute ground pine bark or compost for humus. Water the entire bonsai daily - plant and soil. If you skip a day you may permanently damage the root system. During this period you want to prepare your bonsai for the approaching cold weather of winter. Use reduced rates of fertilizer, and in addition reduce your watering.