Echinocereus rigidissimus subsp. rubispinus
Family: Cactaceae​
​Common Name: rainbow cactus
Origin: E. rigidissimus subsp. rubispinus originates from northern Sonora and northwestern Chihuahua, Mexico, in non-calcareous soils.
Description: The rainbow cactus is a solitary globular cactus with numerous (15-26) ribs, and spines that lay flat against the stems. The rubispinus subspecies is up to 50% smaller than the straight species, and possesses short purple-red spines and stigma lobes. In late spring, a ring of magenta flowers will develop at the head of the cactus, white throated and showy. Up to three months after blooming, flowers will be followed by spiny, green to brown fruits.
  • Interesting Features:
    • Unlike the straight species, the rubispinus subspecies of E. rigidissimus will not turn gray as cacti age, maintaining the vibrant color of spines indefinitely.
  • Uses: The raw fruit of Echinocereus rigidissimus has been used as a source of food by the Chiricahua and Mescalero people, divisions of the North American Apache tribe.

Cultivation and Care:
  • Watering: Low
    • E. rigidissimus subsp. rubispinus is especially susceptible to root rot, and must be watered very sparingly.
    • Occasionally, cacti should be deeply irrigated with rainwater sequestrated with iron, the soil allowed to completely dry in between waterings.
  • ​Soil: The rainbow cactus tolerates poor soil, but grows best in slightly acidic to neutral compost without lime (pH 5 to 7).
    • Provide a very well-draining cactus soil, supplemented with 70-80% sand, grit, pumice, or perlite to aid drainage.
  • Lighting: This species thrives on sun, and should be provided with as much direct light as possible. If indoors, a grow-light may be necessary in order to retain the vibrant color of spines.
  • Propagation: E. rigidissimus subsp. rubispinus propagates through offsets, seed, and by dividing corms, bulbs, rhizomes, or tubers.
    • The surface of cuttings should be allowed to completely callous over before planting, and seeds should be sown after the last frost.
  • Cold Tolerance: 20°F, USDA hardiness zones 9a to 11.
  • Special Accommodations: During the winter, provide cool and dry conditions, in order to observe winter dormancy.
    • While this species can survive a light frost, it should be brought indoors during extreme temperatures.
    • Wear gloves when handling, to avoid damage by the sharp thorns.

Sources:
  1. Llifle Encyclopedia of Cacti
  2. Mountain Crest Gardens
  3. World of Succulents
  4. Native American Ethnobotany Database
  5. Succulents Network
  6. Plant Lust