Cereus repandus f. monstrosus
Synonym: Cereus peruvianus f. monstrosus
Family: Cactaceae​
​Common Name: monstrose apple cactus
Origin: Cereus repandus f. monstrosus is a naturally occurring forma of the straight species, which originates from the tropical and subtropical Americas – likely the western Caribbean and Venezuela or Brazil.
Description: The Monstrose apple cactus is a branching, columnar cactus that grows up to 15 feet (4.6) meters tall. It differs from the straight species by the bumpy, “knobby” stems and copper spines. During early summer, rare and fragrant white flowers can appear, leading to edible orange fruits.
  • Interesting Features:
    • The showy flowers bloom only for a single night before fading.
  • Uses: The crunchy seeds formed from this cacti are called “pitaya” and are commercially cultivated. In Israel, pitaya fruits are becoming an important cash crop during water shortages that threaten conventional orchards.

Cultivation and Care:
  • Watering: Low
    • To establish, water deeply 4 to 6 weeks following planting, and provide supplemental watering every 2 weeks during the first hot summer. After, only water rarely – once or twice every month, with little to no irrigation during winter.
  • Soil: Cereus repandus f. monstrosus grows best in a mineral sandy or gravelly-loam soil. Ensure that soil is very well draining, with an acidic pH preferred (< 6).
  • Lighting: Plant in a hot site with direct sunlight and no shade. However, if grown indoors, gradually introduce the cacti to the heat and sun until acclimated.
  • Propagation: While the Monstrose apple cactus can be propagated both from seed and cuttings, cuttings are the preferred method as seed grown plants mature very slowly. Allow the cutting to fully callous before planting.
  • Cold Tolerance: 20-50°F, USDA hardiness zones 9a to 11b.
  • Special Accommodations: Cereus repandus f. monstrosus is difficult to kill if prevented from root rot and cold damage. As the forma is very frost tender, it should be protected in USDA zone 9 by covering with a blanket during winter.
    • Additionally, provide a liquid fertilizer during the growing season, but do not feed during the dormant winter months.

Sources:​
  1. Mountain Crest Gardens
  2. Llifle Encyclopedia of Cacti
  3. Specialty Produce
  4. Garden Tags
  5. Horticulture Unlimited
  6. World of Succulents
  7. A Fascinating Green World
  8. Plant-Care
  9. SF Gate