Cephalocereus senilis
| Light | Bright light to full sun; the hair helps shield it from intense rays |
|---|---|
| Water | Sparingly; allow to dry fully between waterings, keep dry in winter |
| Soil | Very free-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; ideally never below about 8 °C, USDA zones 9b–11 |
| Propagation | Seed (primary); stem cuttings possible but seldom, as plants rarely branch |
| Toxicity | Non-toxic to cats and dogs |
Cephalocereus senilis, the old man cactus, is a slow-growing columnar cactus native to central Mexico, instantly recognised by the shaggy cloak of long, white, hair-like spines that veils its green stem. Long a staple of houseplant collections, it is prized for that woolly "grandfatherly" coat, which softens the plant's otherwise armed and sharply spined body.
Description
Cephalocereus senilis grows as a slender, unbranched column that stays upright and, over many years, can reach several metres tall in habitat — though potted specimens remain far smaller and grow very slowly. The green stem is divided into numerous low ribs and carries closely set areoles.
The plant's signature feature is its hair: each areole produces a spray of long, fine, white to greyish hairs that drape over the whole stem, densest and most striking on young plants. Beneath this soft-looking veil sit genuine spines that are sharp and can catch skin, so the "fluff" is best admired rather than stroked. In old age the hair can become sparse and matted, and the stem may lose some of its youthful density.
Mature plants — typically only very old, tall ones — develop a woolly cephalium near the top from which the flowers emerge. Nocturnal, funnel-shaped blooms in pale pink, cream, or yellowish tones open at night, but flowering is rare in cultivation because plants must reach considerable size and age first.
Distribution and habitat
The species is native to central-eastern Mexico, chiefly the states of Guanajuato and Hidalgo, where it grows on hot, arid limestone hillsides and canyon slopes. In these exposed sites the dense white hair is thought to help reflect strong sunlight and buffer the stem against heat and temperature swings.
Wild populations have been reduced by illegal collection and habitat loss, and the species is assessed as Endangered on the IUCN Red List. Like the whole cactus family it is listed under CITES Appendix II; nursery-grown plants, however, are widely and legally available and should always be chosen over wild-collected material.
Cultivation
Cephalocereus senilis is an undemanding but slow companion. Grow it in a very free-draining, mostly mineral mix and give it as much bright light as you can — good sun keeps the stem compact and encourages the fullest, whitest hair, whereas too little light causes weak, pale growth. Water thoroughly only once the soil has dried right through, then let it dry again; through winter keep the plant cool and essentially dry to prevent rot.
The hair readily traps dust, and over time the coat can grey or discolour. Growers sometimes gently rinse or lightly comb it to keep it looking fresh, but this must be done carefully because of the sharp spines hidden beneath. Avoid letting water sit in the crown, and provide good airflow. See Watering and Repotting for general technique.
Propagation
Seed is the usual method and, though slow, is straightforward: sow on a warm, mineral surface kept humid until germination, then grow the seedlings on with care. Plants that have been topped, or the occasional branched specimen, can also be propagated from stem cuttings — allow the cut end to callus well before setting it on dry, gritty mix to root. See Propagation — seed and Propagation — cuttings for full walkthroughs.
Common problems
- Rot — the commonest cause of loss, almost always from overwatering, a slow-draining mix, or a cold, damp winter; the stem softens and browns.
- Dingy or matted hair — dust, splashed soil and age can grey the coat; careful rinsing helps, but the effect is partly natural in older plants.
- Etiolation — too little light produces thin, pale growth and sparse hair, spoiling the plant's character.
- Pests — mealybugs are especially troublesome here, hiding easily within the hair; spider mites can also occur. Inspect beneath the coat regularly.
See also
- Cephalocereus — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — cuttings · Pests and diseases