Scientific: Cephalocereus senilis
Common: Old man's cactus
Family: Cactaceae
Origin: Endemic to calcareous canyons within the states of Guanajuato and Hidalgo in eastern Mexico
Ecological update: Cephalocereus senilis is listed as an endangered species in its native habitat.
Pronounciation: Cef-a-lo-SEER-ee-us Se-NIL-is
Hardiness zones:
Sunset 13, 16-17, 21-24
USDA 9 (marginal, protect from cold) to 11
Landscape Use: This curious-looking cactus grown for its odd, woolly appearance. It is used almost exclusively in cactus gardens as a strong visual accent. Old man's cactus is a plant collectors dream worldwide.
Form & Character: Upright, occassionally basally clumping, a real landscape curiosity, timeless.
Growth Habit: Succulent perennial, slow to moderately upright and columnar to 15- to 40-feet tall in its native habitat, seldom branched. Height at maurity is MUCH reduced in Phoenix.
Foliage/Texture: Stems are covered with a dense array of hairs that are modified spines. These hairs give the plant an almost snow-white appearance. Underneath the white hairs are small yellow spines along the aerole ribs; medoium coarse texture.
Flowers & Fruits: Flowers and fruit rarely seen in Phoenix.
Seasonal Color: None
Temperature: Tolerant to 30oF. For frost and light freeze protection, many will cover the apical tips of this cactus with styrofoam cups during cold Phoenix winter nights.
Light: Full sun encourages woolly appearance. Hair production is an adaptational response (increased albedo) to high light intensities of the altiplano, high elevation, region of Mexico where it is indigenuous too and is most prominent on younger plants.
Soil: A well-drained mineral soil is best.
Watering: Water only occasionally if at all during summers.
Pruning: None
Propagation: Tissue culture, grafting, but also relatively easily propagated from elongated softwood stem cuttings of most any length from branched stems. Like other Cereus species, this one will develop roots after directly planting stem cuttings into the soil (right side up!). Make sure to first allow the cut surfaces of the stems to harden for several weeks (callous over) before planting directly into soil.
Disease and Pests: Susceptible to root rot in damp poorly drained soils.
Additional comments: Old man's cactus is a REAL oddity in the landscape. People will pause and marvel at it, especially when younger as the white, woolly hair density is highest when young and decreases with age. The forma cristata is indeed very strange.
