Cephalocereus senilis

Old man cactus is a tall, columnar succulent shrub or tree that is found in the desert or dry shrubland. It is a member of the cactus family (Cactaceae) and has spines that form fine white hairs that are reminiscent of an old man. It is native to Northeastern Mexico but is becoming more challenging to find in its natural habitat. Widespread propagation and popularity in cultivation may reduce the demand on the wild populations. The old man cactus is a popular houseplant and grown for its woolly appearance. The epithet is Latin for "old man."

It prefers a fertile, well-drained soil mix and bright sunlight which encourages the growth of the hair. Water the plants well and allow them to dry out before rewatering. Using an unglazed pot for your indoor planting will allow the excess moisture to evaporate. During the growing season, fertilize it monthly with a balanced fertilizer. If kept well-fed and watered throughout the warmest months, and acclimated to full sun, it can produce 7 inches of growth every year. If grown outside, place it in the full sun. If grown indoors, provide bright light and some direct sun. During the winter water and fertilizer should be withheld. This plant is hardy in USDA Plant Hardiness Zones 9 to 11. The plant will need frost and freeze protection. 

Old man cactus has clusters of stems that may grow to 16 to 40 feet tall; however, the most striking feature is its shaggy coat of long white hairs, hence the common name "old man cactus." The coat is particularly striking on the young cactus, but, as the plant ages, the stem loses its covering. The hairs are modified spines and serve to protect the plant from frost and sun by reflecting the rays of the sun and insulating the cactus from heat and cold. The hairs are only the radial spines of the cactus; beneath them are sharp yellow central spines. The solitary, nocturnal flowers are red, yellow, or white. The plant may not flower for 10 or 20 years or until the plant is over 15 feet tall. The fruits appear 3 to 4 weeks after flowering and are obovoid and rose colored.   

Growing to heights of 40 feet in the wild, when grown as a houseplant it will typically reach a maximum height of 3-4 feet tall. It can take upwards of 200 years for this plant to reach it full height when situated in its natural habitat. For added interest and its unusual wooly appearance, consider adding the old man cactus to your rock or succulent garden.

Diseases, Insect Pests, and Other Plant Problems:  Mealybugs, scale and other flying insects can be an issue because they are difficult to view due to the hairs present on the plant. It is susceptible to fungal diseases such as root rot, if overwatered. If kept damp through cold periods, they will suffer. When moving a houseplant from the house to the outdoors, too much light too soon can cause the plant to become sunburned. Place the plant outdoors for a brief period of time, then gradually increase the sun exposure over a period of several weeks. This will allow the plant to adjust to the increased sunlight.