Melocactus azureus
| Light | Bright light to full sun; acclimate to avoid scorch |
|---|---|
| Water | Moderately in warm growth; keep nearly dry and warm in winter |
| Soil | Gritty, fast-draining mineral mix with added limestone/grit (see Soil and potting mix) |
| Temperature | Warmth-loving; keep well above freezing, ideally above 10 °C |
| Propagation | Seed |
| Toxicity | Non-toxic to cats and dogs |
Melocactus azureus is a striking blue-glaucous "melon cactus" from the interior of Bahia, in northeastern Brazil, prized among collectors for its chalky, powder-blue body set against stiff, dark spines. Like all members of the genus Melocactus, a mature plant stops enlarging its green body and instead crowns itself with a woolly, bristly cephalium from which the flowers and fruit emerge, giving rise to the common name blue melon cactus.
Description
Melocactus azureus forms a solitary, roughly globular to shortly barrel-shaped body reaching up to about 30 cm tall and around 14–20 cm in diameter, divided into about nine or ten prominent ribs. The surface carries a distinctive waxy, bluish bloom that gives the plant its name; beneath it the skin is deep green to grey-green, and the bloom is easily rubbed away by handling. Along the ribs sit widely spaced areoles bearing a few stout, straight to slightly curved spines that are dark grey to nearly black when young, contrasting handsomely with the blue body.
On reaching maturity the plant develops a terminal cephalium — a dense cap of white wool and reddish bristles. Once this forms the green body no longer grows taller; all further increase is in the cephalium, which slowly rises over the years. Small pink to magenta flowers appear at the top of the cephalium and are followed by slender, whitish to pale pink, berry-like fruits.
Distribution and habitat
The species is native to a restricted area of the state of Bahia in northeastern Brazil, where it grows on open, sun-baked limestone outcrops and stony ground in seasonally dry caatinga-type vegetation. In habitat it endures strong sun, high heat and a long dry season, rooting into shallow, alkaline, mineral soils among rock.
Because its natural range is small and fragmented and subject to habitat loss from agricultural clearing, wild Melocactus azureus is assessed as Endangered on the IUCN Red List, and — like the whole cactus family — the genus is listed under CITES Appendix II. Nursery-grown, seed-raised plants are widely available and entirely legal to own and trade; collecting from the wild is not.
Cultivation
Melocactus azureus rewards a warm, bright, dry-loving regime and dislikes cold, damp conditions. Grow it in a very free-draining, mostly mineral mix; a little added limestone or calcareous grit suits its naturally alkaline home ground. Give it the brightest position you can — up to full sun once acclimated — as strong light keeps the body compact and helps preserve the prized blue bloom.
Water moderately through the warm growing season, letting the soil dry out between waterings, then keep the plant nearly dry and warm over winter. This is a distinctly warmth-loving cactus: it is far less cold-tolerant than many desert species and is easily lost to rot if kept wet and cool. Handle sparingly, since fingerprints and abrasion mar the waxy coating. See Watering and Repotting for general technique.
Propagation
Melons are grown from seed, and M. azureus is no exception. Sow onto a warm, mineral surface and keep humid until germination; seedlings appreciate steady warmth and bright light as they establish. Because a solitary plant does not offset and cannot be divided once it has formed a cephalium, seed is effectively the only practical method. See Propagation — seed for a full walkthrough.
Common problems
- Rot — the commonest cause of loss, almost always from overwatering, a slow-draining mix, or cold damp conditions; the body softens and discolours from the base.
- Loss of bloom — the blue waxy coating is easily rubbed off by handling and does not regenerate on old growth, so minimise contact.
- Etiolation — too little light makes the body elongate and turn a duller green, spoiling the compact blue form.
- Pests — mealybugs (white fluff in the areoles and roots) and red spider mites (fine webbing, bronzed skin) are the usual offenders; see Pests and diseases.
See also
- Melocactus — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Pests and diseases