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.
A few different tricks help these plants handle the desert conditions. The sharp spines that you see on cactus and some other plants help shade the plant from the sun, keeping it cool. Certain plants like mesquite trees grow very long tap roots, reaching down over 100 feet to reach the groundwater, water stored deep underground.