Cereus aethiops
| Light | Bright light to full sun once established |
|---|---|
| Water | Moderate in growth; keep dry through winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Cuttings, offsets or seed |
| Toxicity | Non-toxic to cats and dogs |
Cereus aethiops is a slender, branching columnar cactus from Argentina, prized in collections for the striking contrast between its blue-grey, waxy stems and its dark, almost black spines. Young growth is especially blue-glaucous, and as the clumps age they build into a cluster of upright stems topped in season by large, night-opening flowers. It belongs to the genus Cereus and is sometimes still traded under the older name Cereus coerulescens.
Description
Cereus aethiops forms an erect, shrubby plant that branches from the base and, with age, from higher up the stems, eventually reaching a metre or more tall in cultivation. Individual stems are relatively slim compared with many in the genus, with several prominent ribs and a distinctly bluish, waxy bloom that is most vivid on new growth and can fade to greener grey on older wood.
The areoles carry spines that are dark brown to black when young, often paling and greying with age. It is this dark spination set against the cool blue stems that gives the species its ornamental appeal. Like other Cereus, it produces large funnel-shaped flowers that open at night; the blooms are pale, typically whitish flushed with pink on the outer segments, and are followed by fleshy fruit.
Distribution and habitat
The species is native to Argentina and neighbouring Uruguay. In Argentina it ranges widely, from the northern and central provinces south into northern Patagonia, growing in arid and semi-arid scrub and rocky ground. In habitat it experiences hot, dry summers and cool winters, rooting in lean, sharply drained soils among rocks and low shrubs. Its natural tolerance of a genuine cold-but-dry winter rest is worth remembering when growing it.
Cultivation
Cereus aethiops is an easy and vigorous grower, well suited to beginners. Plant it in a gritty, mostly mineral mix and give it as much light as you can — plenty of sun brings out the bluest stem colour and the darkest, healthiest spines, whereas too little light produces thin, pale, drawn growth.
Water moderately through the warm growing season, letting the mix dry out well between waterings, and then keep the plant dry and cool over winter to firm up the growth and encourage flowering. It is robust and columnar, so a heavier pot and eventual repotting into a stable container help support taller clumps. See Watering for general technique.
Propagation
Propagation is straightforward. Stems and branches root easily as cuttings: sever a length, let the cut end callous over for a week or so in a dry, shaded spot, then set it on a barely moist mineral mix until roots form. Basal branches can be removed and treated the same way, essentially as offsets. The species also grows readily from seed, though seedlings are slower to reach flowering size than rooted cuttings.
Common problems
- Rot — the main risk, almost always from overwatering or a poorly draining mix, especially if the plant is watered while cold in winter.
- Etiolation — insufficient light causes thin, pale, stretched growth and washes out the prized blue colour and dark spines.
- Pests — mealybugs (white fluff in the areoles and around the roots) and red spider mites are the usual offenders; see Pests and diseases.
See also
- Cereus — the genus overview
- Grafting · Soil and potting mix · Watering · Propagation — cuttings