Cephalocereus senilis, commonly known as Old Man Cactus, is one of the most popular and identifiable Cactus family members. It is native to Mexico in areas such as Guanajuato and Hidalgo, located in the east. The fine white hairs cover the entire fleshy columnar body and hide the sharp spines. Aside from its charm, the hair serves an important purpose. It protects against the harsh desert sun, which is common to this plant's native home.
This cactus can go outside in USDA hardiness zones 9 and 10. Native to Mexico, it needs hot, dry climates and bright sunlight. The plant uses long hair to keep itself cool in its natural habitat. As an outdoor plant, it can get 45 feet (13.7 m) tall but is generally slow-growing as a potted plant.
Old Man Cactus is mostly grown as a houseplant. It stays small and is easily kept in containers for their entire lives. Indoor cactus growing requires a sunny window and temperatures of at least 65 ˚F (18 ˚C). Give it a winter hibernation period in an area below 65 ˚F (18 ˚C) for best growth.
Use a cactus mix or blend of sand, perlite, and topsoil for indoor cactus growing. Also, use an unglazed pot for growing Old Man Cactus. This will allow the pot to evaporate any excess moisture. Old Man Cactus likes its soil on the dry side. Overwatering is a common cause of rot and disease.
Allow the top couple of inches of the soil to dry out completely between waterings. In winter, reduce watering to once or twice during the season.
Fertilize with cactus food in early spring, and you might be rewarded with thick pink flowers. In its natural habitat, this cactus grows a pinkish-red fruit, but this is rare in cultivation.
Old Man Cactus needs a sunny, warm location but has few other needs. You should watch it carefully for pests, however, which can hide in the hair. These include mealybugs, scale, and flying pests.
Old Man Cactus is easy to propagate from seeds and cuttings.
Seeds take a long time to grow into something recognizable as a cactus, but it is a cheap and fun project.
Cuttings need to lie out on the counter in a dry location for a couple of days to callus. Then insert the cut end with the dry, white callus into a soilless medium, such as sand or perlite. Keep the cutting in moderate but not scalding light where temperatures are at least 70 ˚F (21 ˚C) for best rooting. Do not water until the little cutting has rooted. Then treat your new Old Man Cactus as you would a mature specimen.