Espostoa melanostele
| Light | Bright light to full sun once established; acclimatise gradually |
|---|---|
| Water | Moderate in the growing season; keep dry and cool in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Seed; offsets from the clustering base |
| Toxicity | Non-toxic to cats and dogs |
Espostoa melanostele is a densely white-woolly columnar cactus from the western slopes of the Peruvian Andes that often clusters from the base to form a small forest of fluffy stems. Its columns are wrapped in fine, dense white hair that softens the plant's outline and gives it the affectionate common name Peruvian old lady cactus. It is one of the most widely grown members of the genus Espostoa, and was long placed in its own genus as Pseudoespostoa melanostele.
Description
Espostoa melanostele forms erect, ribbed columns that in cultivation typically reach a metre or so in height and around 8–10 cm in diameter, branching and offsetting from the base to build a clustered clump over time. The stem is divided into many low, closely-set ribs, each carrying densely packed areoles.
The whole plant is cloaked in long, silky white hairs that all but hide the body, interspersed with slender spines — the central spines are stiffer, often yellowish to amber, and project through the wool. The dense white covering is not merely ornamental: in habitat it shades the stem from fierce high-altitude sun and buffers it against cold nights.
As a mature plant approaches flowering age it develops a cephalium — a specialised lateral zone of dense wool and bristles, often tinged darker, from which the flowers emerge. The nocturnal flowers are pale, whitish to cream, and open at night, followed by small fleshy fruits. Flowering is uncommon on young or small plants.
Distribution and habitat
The species is native to Peru, where it grows on rocky, sun-baked slopes and in dry inter-Andean valleys on the western side of the Andes, often at considerable elevation. These are bright, arid to semi-arid habitats with strong sunlight, sharp drainage and pronounced day–night temperature swings — conditions the plant's heavy wool coat is well adapted to.
Cultivation
Espostoa melanostele is one of the more forgiving woolly columnar cacti and a rewarding plant for a sunny windowsill or greenhouse. Grow it in a very free-draining, mostly mineral mix and give it as much light as you can; strong light keeps the wool dense and white, whereas too little produces sparse hair and weak, etiolated growth. Acclimatise plants gradually when moving them into full sun to avoid scorching.
Water moderately through the warm growing season, always letting the mix dry out well between waterings, then keep the plant dry and cool over winter to firm up growth and encourage eventual flowering. Avoid letting water and debris sit in the wool, which can encourage rot or discolouration. See Watering and Repotting for general technique.
Propagation
The species can be raised from seed, which germinates well on a warm, gritty surface kept humid until the seedlings establish. Because the plant clusters freely, it is also readily increased from offsets: detach a basal branch, let the cut surface callus for several days to a couple of weeks, then pot it into a dry, gritty mix and water sparingly until roots form.
Common problems
- Rot — usually from overwatering or a poorly-draining mix; the stem softens and discolours, often from the base.
- Grubby wool — dust, algae and mineral deposits can dull the white hair over time; keeping the plant dry-topped and well-lit helps preserve its colour.
- Etiolation — too little light gives thin, sparse wool and pale, stretched growth that loses the plant's characteristic fluffiness.
- Pests — mealybugs are especially troublesome because they hide easily within the dense wool; red spider mites can also occur in hot, dry conditions.
See also
- Espostoa — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Repotting