Echinocereus rigidissimus var. rubrispinus

Botanical Name — Echinocereus rigidissimus var. rubrispinus 

Common Name — Arizona rainbow cactus, rainbow hedgehog cactus

Plant Family — Cactaceae

Background

Rainbow hedgehog cactus is easily one of the most fun common names I’ve come across. This petite plant typically grows to reach 30 cm tall by 11 cm wide. Aptly named, it bears new spines that are magenta colored and fade to yellow or light pink with maturity. Where it is endemic,  parts of northwest Mexico and the southwest United States, it can be found growing on rocky slopes at high elevation. Echinocereus rigidissimus grows as a stocky, solitary stem, rarely producing and offsets.

Growth Requirements

Sun

• Echinocereus rigidissimus are desert cacti that require full sun. Eight hours of direct sunlight a day is ideal but at a minimum, these plants should be provided with at least five hours. 

Temperature/ Humidity 

• Arizona rainbow cacti thrive in warm temperatures and low humidity. They will thrive in temperatures above 70 ºF. 
• They can be very cold tolerant, hardy to 10 ºF. As temperatures cool, watering should be gradually reduced. 

Water

• Echinocereus rigidissimus plants are extremely drought tolerant. Water them thoroughly, fully saturating the soil. Always allow the soil to dry out completely in between waterings. 
• If you are unsure whether or not the soil is dry, wait a few days before watering. It is much better to underwater than overwater. Excessive moisture can quickly lead to root rot.

Soil/Roots

• These plants prefer a gritty, sharply draining mix. Use cactus soil or amend regular potting mix with sand and fine pumice up to 50% to improve texture and drainage. 
• In desert climates, these plants can be potted directly in the earth and grown outdoors year-round. 

Flowering

• Echinocereus rigidissimus var.  rubrispinus flower in the spring, from late April to early June. Flowers are buds are borne in clusters from the top if the cacti. Blossoms are bright pink in color. 
• These cacti are less likely to flower when grown indoors. To improve chances of watering, ensure the plant is given excellent light conditions and avoid watering during the winter. 

Fertilization

• Rainbow hedgehog cacti do not require fertilization, however, a boost of nutrients during the growing season will help them thrive. Use a fertilizer formulated specifically for cacti and succulents, once a month, during the spring and summer only. 

Propagation

• Since this plant rarely produces offsets, seed is the most reliable way to propagate. For best results use freshly harvested seeds. Keep soil moist, not soggy, to encourage germination and while young plants are establishing themselves. 

Health
Diseases

• These cacti are not especially prone to pests and diseases. Root rot can easily occur if the plant is overwatered. Keep an eye out for common pests such as mealybugs, aphids, and scale. 

Maintenance (pruning, legginess, repotting)

• These hardy plants require very little maintenance. Container grown cacti prefer to be rootbound, so repotting should be necessary only once every 2 to 3 years. Repot into a planter 2” larger in diameter to give the plant plenty of room to continue growing. 

Toxicity

• Echinocereus rigidissimus cacti are not known to be toxic to humans and pets.