Pachycereus schottii aka Old Man Cactus

Senita cactus is a slow-growing columnar species that typically reaches 1-3 meters in cultivation and up to 6.5 meters in old wild specimens, with individual stems 5-10 cm in diameter. It branches at the base to form thickets, so mature plants spread several meters wide. Each stem carries 4-13 ribs, with shaggy gray "old man" spines on upper flowering portions.

Senita is a Sonoran Desert species native to northwestern Mexico (Sonora, Sinaloa, Baja California, Baja California Sur) and just barely extends into the United States, where it is known only from about nine sites at Organ Pipe Cactus National Monument in southern Arizona. It grows on sandy and gravelly soils in desert washes at elevations from sea level to about 800 meters.

In the wild, senita relies on winter and late summer rainfall, and established landscape plants need only minimal irrigation. Treat it as fully drought-tolerant: water sparingly and let the soil dry completely between waterings, especially in cooler months when the plant is not actively growing.

Senita prefers sharply drained, sandy or gravelly soils — the same conditions it occupies in desert washes between 400 and 500 meters elevation. A well-drained mineral cactus mix or native desert soil works in cultivation; avoid heavy, water-retentive substrates.

The species is hardy in roughly USDA zones 9-10 and prefers temperatures above -4°C (25°F); Arizona clones can tolerate brief frosts down to about 15°F (-9°C), though the growing tips need protection. The popular spineless "totem pole" monstrose form is more cold-sensitive and should not see temperatures below about -4°C.

Senita flowers are small (2.5-5 cm long), funnel-shaped, and white to deep pink. They open after sunset for only six to twelve hours and close by mid-morning, with each flower lasting only a single night. Blooming runs from late March through September, and flowers emerge from the bristly pseudocephalium near the top of mature stems.

The most widely grown horticultural form is the spineless monstrose cultivar commonly sold as the "totem pole cactus," which has lumpy, knobby stems and is more cold-sensitive than the wild type. Older taxonomy treats the species under Lophocereus schottii, and many growers and references still use that name.

Site it in full sun on sharply drained sandy or gravelly soil — desert wash conditions are ideal — and water sparingly once established. Provide some overhead protection or choose a hardier Arizona clone if winter lows approach 15°F (-9°C).

In the wild, Arizona populations show very little seedling recruitment and persist mainly through vegetative branching at the base. In cultivation the species is most easily propagated from stem cuttings, which root readily in dry, well-drained substrate; seed propagation is also possible but slower.

Senita has an obligate mutualistic relationship with the senita moth (Upiga virescens) that closely parallels the yucca-yucca moth system. The moth is the only nocturnal pollinator of the cactus and is responsible for 75-95% of fruit set; daytime bees account for the remainder. Flowers open after sunset for 6-12 hours, female moths actively deposit pollen using specialized abdominal scales, and the moth's larvae develop inside a portion of the resulting fruit.

The spherical red fruits are edible — 1-4 cm across with bright red, fleshy pulp described as tasty — and are eaten raw when fully ripe. Despite being palatable, they are only occasionally consumed and are not a major food source.

The five-ribbed sterile/juvenile stems are highly valued in Mexican traditional herbal medicine, where they are used for ailments including diabetes, tuberculosis, stomach ulcers, cancer, hair loss, and poor circulation, and applied externally to wounds and sores. A common preparation is a roughly 20 mm cross-section of stem cooked in one liter of water and drunk throughout the day. Note that traditional uses are not the same as clinically validated treatments.

Beyond traditional medicine, senita has attracted research attention for its phytochemistry: tissues contain tetrahydroisoquinoline alkaloids (notably lophocerine and pilocereine), triterpenes, sterols, and flavonoids, and laboratory studies have demonstrated cytotoxic activity on human carcinoma cells (9KB line) and antitumor effects in mice.

With a bit of knowledge and dedication, you can successfully care for Old Man Cactus, making it a rewarding choice for those seeking a moderate challenge.

Old Man Cactus thrives in bright and direct sunlight. To ensure your plant receives enough light to survive, place it less than one foot from a window. The current weather in your area may affect the placement in your home. For example, if you live in a region that has longer and more intense periods of sunlight, then you may want to place the plant farther away from the window to avoid direct sunlight and reduce the risk of sunburn. Alternatively, if you live in a region with relatively milder temperatures and less intense sunlight, then you may be able to place the plant closer to the window for increased exposure. Ultimately, the current weather in your area should be taken into consideration when determining the best placement for your Old Man Cactus.

No verified data on the toxicity of this plant exists within Ploi's records. Should you, someone in your family, or your pet ingest plant material with an unknown toxicity level, it is recommended to seek medical advice.

During the wintertime, it is common for Old Man Cactus plants to go dormant and their growth rate may slow down. Therefore, the amount of waterings should be spaced out more.