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.
Water the cactus based on your environment and the time of year. A good method is to water a cactus as follows: Dry climate, outdoors: Water every two to three days when warm and sunny; Humid, cool or indoors: Water every week; During the fall and winter months, the plants should be watered less frequently in order to promote blooming.