The mineral part may be vermiculite, perlite, builders sand, pumice or a combination of any two or three. The organic part may be peat, fir bark, pine bark or a combination of any two or three. Soilless mixes provide and excellent environment for growing healthy roots. They also need special attention to watering and fertilizing. Mix together one part good garden soil, one part peat moss, and one part perlite or coarse builders sand.
Soil based mixes tend to be a little more forgiving in regards to moisture and fertilizing.
Containers should be filled to within about one inch of the top to allow room for water.