Carnegiea gigantea
| Light | Full sun; young plants appreciate light shade from a nurse plant or filtered exposure |
|---|---|
| Water | Sparingly; soak only when the soil has dried completely, keep dry through winter |
| Soil | Very gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Hardy to light frost when dry; USDA zones 9a–11 |
| Propagation | Seed (the standard and only practical method) |
| Toxicity | Not classified as toxic to cats or dogs; the stiff spines are the main hazard |
Carnegiea gigantea, the saguaro, is the emblematic tall, arm-bearing cactus of the Sonoran Desert and the sole species of the genus Carnegiea. A single mature plant can tower several metres high on a fluted, columnar trunk, eventually raising the curved side branches that give the species its unmistakable silhouette. It is famously slow-growing and long-lived, protected under law in Arizona and ranging south into northern Mexico, and treasured in cultivation as much for its patience-testing pace as for its grandeur.
Description
Carnegiea gigantea is a massive tree-like cactus that in age forms a stout, ribbed column topped with one or more upcurved arms. The trunk is deeply pleated into numerous vertical ribs lined with clusters of stiff spines; the ribs act like an accordion, letting the plant swell with stored water after rain and contract again through drought. The flesh is supported internally by a ring of woody ribs that persist as bleached "cactus skeletons" long after a plant dies.
Large white flowers open near the tips of the stems in late spring, each with a ring of waxy petals around a dense boss of yellow stamens. They open at night and stay open into the following morning, offering nectar to bats, birds and insects. The flowers give way to fleshy red fruit packed with tiny black seeds, an important seasonal food for desert wildlife and, historically, for the region's Indigenous peoples.
Saguaros grow with legendary slowness. A seedling may take many years to reach even a few centimetres, and plants typically do not begin producing their first arms until they are already decades old and well over head height. The very largest specimens are well over a century in age.
Distribution and habitat
The saguaro is native to the Sonoran Desert, ranging across southern Arizona and into the Mexican state of Sonora, with a small toehold in southeastern California. It grows on rocky bajadas, desert flats and gravelly slopes, often in the shelter of "nurse plants" such as palo verde or mesquite whose shade protects vulnerable seedlings from sun and frost.
The species is closely tied to a narrow climate: it needs the Sonoran Desert's biphasic rainfall and is intolerant of hard, prolonged freezes, which limits its natural range. Saguaros are protected under Arizona law, and harvesting, damaging or moving wild plants is strictly regulated. As with the whole cactus family, the genus is listed under CITES. Nursery-grown plants raised from seed are legal to own and trade; collecting from the wild is not.
Cultivation
In cultivation the saguaro is grown far more often than it is successfully grown large — its glacial pace means most collectors keep it as a slow, characterful pot plant rather than expecting a towering specimen. Give it the brightest position available; in habitat it is a full-sun plant, though very young seedlings do better with a little shade, mimicking the protection of a nurse plant.
Plant it in a very gritty, mostly mineral mix in a container with excellent drainage. Water thoroughly only once the soil has dried right out during the growing season, then allow another dry spell before repeating. Keep the plant dry through the cold months, as cold combined with damp is the surest way to lose it. Where winters are mild and dry, established plants tolerate light frost, but wet cold causes rot. See Watering and Repotting for general technique; repot infrequently, as this species resents disturbance and grows slowly into its pot.
Propagation
Seed is the standard method, and effectively the only practical one — saguaros do not offset and are not grown from cuttings. Sow the fine seed on the surface of a warm, damp mineral mix and keep it humid and bright; germination is usually good, but the seedlings are tiny and grow with famous slowness, needing steady warmth and patience over many years. Some growers speed up early growth by grafting young seedlings onto a faster columnar rootstock before returning them to their own roots. See Propagation — seed for a full walkthrough.
Common problems
- Rot — the leading cause of loss, almost always from a cold, wet root run or a slow-draining mix; the base softens and discolours.
- Cold damage — hard or prolonged frost, especially on a wet plant, scars or kills the tissue; keep the plant dry and sheltered in winter.
- Etiolation — too little light makes the stem thin, pale and drawn, spoiling the characteristic stout, ribbed form.
- Pests — mealybugs (white fluff among the spines and ribs) and, under glass, red spider mites are the usual offenders. See Pests and diseases.
Legal status
The saguaro is protected under Arizona's native plant laws. Wild plants may not be collected, moved or destroyed without permits, and the species is a conservation icon of the American Southwest. Internationally, like all cacti, Carnegiea gigantea is covered by CITES controls on trade. None of this restricts ownership of nursery-propagated, seed-grown plants, which are the only legitimate source for growers.
See also
- Carnegiea — the genus overview
- Sonoran Desert · CITES
- Grafting · Soil and potting mix · Watering · Propagation — seed · Repotting · Pests and diseases