About 5 years ago, Sheridan Cleland of MyPDFscripts wrote the below article on his blog. Soon after, the site disappeared. I wanted to keep the memory alive, because these practices by the studios have not changed. They have only become worse.
Cacti are one of my favorite types of plants to grow inside all year and outside in summer. Unfortunately, the ambient air tends to stay moist during most seasons, a condition which makes cacti unhappy. Cactus potting soil can enhance drainage, increase evaporation and provide the dry conditions that cacti favor.
Cactus potting soil is available in most nurseries and garden centers. It forms a better basis for cactus roots than regular soil and keeps roots and stems from sitting in moisture, which can cause rot. The right planting mix for cactus plants has superior drainage and will dry out quickly after watering.