Christmas cactus is not considered poisonous to cats, but it's still best to keep them out of your cat's reach. While the Christmas cactus itself is not harmful to cats, the soil in which it's grown could contain fertilizer or other substances that could be dangerous if ingested. Additionally, some cats might be tempted to chew on the leaves, which could cause stomach upset or other gastrointestinal issues. To be safe, it's best to keep the Christmas cactus out of reach and keep an eye on your cat if they do come into contact with it.