Cactus · Sonoran native
Senita
Pachycereus schottii · Cactaceae
Also called: Old Man Cactus, Whisker Cactus, Garambullo, Sinita
Senita (Pachycereus schottii) is a very low-water cactus native to the Sonoran Desert region well suited to Tucson and the low desert. It thrives in full sun, with a slow to moderate growth rate.
Senita at a glance
- Water use
- Very Low (established)
- Sun
- Full sun; tolerates intense heat and reflected heat.
- Mature size
- 8-15 ft H x 8-12 ft W (multi-stemmed columnar clump from the base)
- Growth rate
- Slow to moderate
- Bloom
- Pale pink to whitish (small night-blooming flowers borne among the gray bristles on older stem tips), Spring through summer; flowers open at night. Small red edible fruits follow.
- Cold hardiness
- Tender; tolerates only brief lows around 25-30 F (USDA zones 9b-11). Frost sensitive - best in warm protected microclimates in Tucson.
- Soil
- Well-drained rocky, gravelly, alkaline desert soils; requires sharp drainage and dislikes wet feet.
- Native range
- Sonoran Desert; in the U.S. restricted to a small area of extreme south-central Arizona (Organ Pipe Cactus National Monument area), with a broad range through Sonora and Baja California, Mexico. (Accepted name Pachycereus schottii; Lophocereus schottii is a synonym.)
- Best used as
- Specimen / vertical accent, Architectural focal point in warm xeric gardens, Wildlife habitat plantings
- Wildlife
- Classic example of an obligate mutualism with the senita moth (Upiga virescens), its specialized pollinator; also visited by bats and bees. Fruit eaten by birds and other wildlife.
- Toxicity
- Non-toxic; small fruits are edible. Bristly spines on mature stems are a physical hazard.
How to grow Senita in Tucson & the low desert
Watering
Very drought tolerant once established; occasional deep watering (roughly monthly) in peak summer encourages growth, none needed in winter. Keep dry in cold weather.
Fertilizer & nutrients
Little to none required; an optional light spring feeding with low-nitrogen cactus fertilizer during active growth. Avoid fall/winter fertilizing.
Pruning & care
No routine pruning; remove only frost-damaged, rotted, or diseased stems with clean tools at a joint.
Notes
Named for the shaggy gray bristles ('whiskers' / 'old man' beard) that develop at the tops of mature, flowering stems. Multiple bluish-green ribbed columns branch from the base. Frost tenderness limits it to protected sites in the Tucson area; wild Arizona populations are very localized and protected.
Sources: Arizona-Sonora Desert Museum; Organ Pipe Cactus National Monument / NPS; University of Arizona Cooperative Extension; Plants of the World Online (Kew) for accepted nomenclature