As with any cactus, they need well-draining soil, but of any species these do best in a highly inorganic mix. I use a mix very similar to my mesembs, which is roughly 75% pumice and 25% organic material – typically a mix of orchid bark and cactus soil.
In summer, during their growing season, they can take water somewhat regularly. I judge how much and how often to water mine by appearance: if they’re looking wrinkled and deflated, it’s probably time to give them a deep drink.
