Identifying a Sentimental Cereus tetragonus "Fairy Castle"

Initial Assessment

The plant is likely a succulent rather than a true cactus—spine structure would confirm. Notably, the colorful flowers appear to be straw flowers (dried blooms glued on by retailers), not the plant's natural flowers.

Immediate Care (Winter Dormancy)

• Water very infrequently.
• If cactus: no water during winter dormancy.
• If succulent: water only when soil is completely dry or stems feel slightly soft.

Identification Breakthrough

The owner correctly identified it as Cereus tetragonus (Fairy Castle Cactus), native to Brazil, genus Acanthocereus. This matches the care advice given: minimal winter water, well-draining soil, bright light.

Ongoing Care

• Repot in spring with cactus/succulent mix.
• Provide maximum sunlight.
• Water thoroughly but only when bone-dry during growing season.
• No fertilizer in winter.

A lovely legacy plant—your mother would be pleased it's in caring hands.