British Cactus and Succulent Society on Twitter: "It benefits from well-drained compost and is watered from mid-March to end-September. At other times, keep it completely dry. It is slow growing – only
Cactus ottonis
The New Cactus Lexicon Illustrations | NHBS Academic & Professional Books
Cactus Lexicon by Curt Backeberg (1978-04-24): Amazon.com: Books