Cactus
Old Man Cactus
Cephalocereus senilis · Cactaceae
Also called: Old Man of Mexico, White Persian Cat Cactus, Bunny Cactus, Viejito
Old Man Cactus (Cephalocereus senilis) is a low-water cactus well suited to Tucson and the low desert. It's a slow-growing cactus.
Old Man Cactus at a glance
- Water use
- Low (established)
- Sun
- Bright light with protection from intense afternoon sun in Tucson. Despite its insulating white hair, it sunburns if abruptly exposed; provide filtered light or morning sun with afternoon shade, and acclimate slowly. Often grown in a container that can be sited under cover.
- Mature size
- Columnar and slow; in cultivation usually 1-3 ft tall over many years (can reach 10+ ft in habitat over decades). Stays a manageable container size locally.
- Growth rate
- Slow
- Bloom
- Pinkish to pale yellow nocturnal flowers - but flowering occurs only on very old, tall (15+ ft) plants, so essentially never in Tucson cultivation., Rarely if ever blooms in cultivation; would be late spring/summer at night on mature habitat plants.
- Cold hardiness
- Frost-tender; keep above about 40-45 F and protect from any frost. In Tucson treat it as a tender container plant - move it under cover or indoors during winter cold snaps and freezes (USDA 9b minimum, and only with reliable frost protection).
- Soil
- Very gritty, fast-draining mineral cactus mix; it favors alkaline/limestone soils, so Tucson's calcareous soils suit it. Excellent drainage is critical.
- Native range
- Native to limestone canyons of Guanajuato and Hidalgo in east-central Mexico; not a desert Southwest native.
- Best used as
- Specimen/novelty container plant, Protected patio accent, Collector cactus, Indoor bright-window plant
- Wildlife
- Minimal wildlife value in Tucson; an ornamental novelty.
- Toxicity
- Non-toxic to people and pets. The fine white hairs conceal sharp yellow spines beneath, which are the real hazard.
How to grow Old Man Cactus in Tucson & the low desert
Watering
Water sparingly only when soil is fully dry (about every 2-3 weeks in summer); keep nearly dry and do not water through cool, damp winter weather. Overhead watering mats and discolors the white hairs, so water at the base.
Fertilizer & nutrients
Feed lightly with a dilute, low-nitrogen cactus fertilizer once or twice during the spring-summer growing season; do not feed in winter.
Pruning & care
None needed. Do not trim the hairs. Gently rinse/comb dust from the hairs occasionally to keep them white.
Notes
Grown in Tucson chiefly as a potted novelty for its shaggy white 'hair.' Two cautions: slow-acclimate to sun to avoid scald, and overwinter under cover - it has essentially no frost tolerance unlike most desert cacti.
Sources: NC State Extension Gardener Plant Toolbox - Cephalocereus senilis; World of Succulents / Global Ideas - Cephalocereus senilis care; Planet Desert - Old Man Cactus (Cephalocereus senilis)