How is “potting soil” different from regular soil?
Kim’s answer is correct. Depending on what brand of potting soil you use, the contents will vary. Sometimes crushed white styrofoam is used to make potting soil lighter. The other item often used to make the soil lighter in higher quality potting soils is perlite. Perlite is natural and has no chemical reactions as an inert, “glass” type substance with a balanced PH of near 7. A volcanic ore is mined, then the ore is rapidly heated to a very high temperature causing the ore to expand like popcorn. The expansion process contributes to the white color, whereas the original ore may have been a glassy dark or gray color. For the most part, perlite contains its silicon [silicon is an abundant element used to make glass (from sands)], but perlite also contains other minerals such as aluminum, potassium, trace minerals, sodium, calcium, magnesium. In horticultural applications, perlite is used throughout the world as a component of soilless growing mixes where it provides aeration and optimum
