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.
Soil for cacti can be prepared at home. While no soil mix is perfect in all situations for all plants, a good, standard soil recipe for cactus is 20 percent top soil to 10 percent peat moss to 70 percent pumice or vermiculite. Add a half cup of bone meal for every 12 quarts of soil mix to ensure a proper pH balance.