E. rigidissimus ssp. 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.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.
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. Temperatures down to 20°F are tolerated (USDA hardiness zones 9a to 11), but cool and dry conditions should be provided during the winter to observe dormancy. Although this species can survive a light frost, it should still be brought indoors during extreme temperatures.
E. rigidissimus ssp. 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.
