As of August 2014, at least 48 manufacturers produce potting soil in the United States, including Grab N' Grow, Bio Com, Compost USA, Blackjack Soil Company, Pine Products, Creekside Soils, Green Country Soil, Dr. Earth, Graco Fertilizer, Master Mix and United Agricultural Service. Potting soil is enriched topsoil made from loam, sand, peat and nutrients that helps potted plants start their life cycle before developing full-fledged root systems.
Good potting soil meets all of a plant's nutritional requirements, according to the University of Connecticut's College of Agriculture and Natural Resources. Potting media has the right structure of support, drainage, nutrition, water retention and air circulation to achieve this. Potting soil can also include bark, Styrofoam, moss, perlite, vermiculite, water retention crystals and compost. Some varieties are sterilized to kill bacteria and weeds before packaging.
Some potting soils are made for specific plants such as orchids and cacti. Even if fertilizers are present in the original potting soil, more may need to be added later to enrich the plant's environment. The pH of the soil must also be monitored to ensure the plant grows properly. Larger houseplants may need sturdier soils that include mineral-based substances. Potting soils must eventually be replaced with normal soil once larger plants outgrow their pots.