Mammillaria hahniana
| Light | Bright light with a few hours of full sun; some shade from the harshest afternoon sun |
|---|---|
| Water | Moderately in the growing season, allowing to dry fully between waterings; keep dry and cool in winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Seed; offsets from older clustering plants |
| Toxicity | Non-toxic to cats and dogs |
Mammillaria hahniana is a small, globular Mexican cactus wrapped in long, silky white hairs and bristles, an appearance that has earned it the affectionate common name Old Lady Cactus. Starting out solitary and rounded, it slowly clusters into a low mound with age, and in spring crowns itself with a neat ring of small pinkish-purple flowers set against the white wool.
Description
Mammillaria hahniana forms a firm, flattened-globular body typically up to about 10 cm across, at first solitary but in time offsetting to build a cushion of heads. Like other Mammillaria, the body is covered in spirally arranged tubercles rather than continuous ribs. Each tubercle bears an areole tipped with short whitish radial spines, and — most distinctively — long white hairs that arch over the plant and give it a shaggy, silvery coat. The density and length of this hair varies considerably from plant to plant, and the hairiest forms are the ones most prized in collections.
The flowers appear in spring, sometimes with a lighter flush later in the year, forming a characteristic crown or ring near the top of the plant. They are small, funnel-shaped and deep pink to purplish-red, and are often followed by slender pink or reddish seed pods that emerge from between the tubercles.
Distribution and habitat
The species is native to central Mexico, where it grows in the semi-arid highlands of states such as Guanajuato and Querétaro. It is typically found on rocky slopes and among limestone outcrops in open scrub, rooting in shallow, gritty soils that drain quickly after the seasonal rains. The dense white hair is thought to help shade the body and reduce moisture loss under strong highland sun.
Cultivation
Mammillaria hahniana is one of the easier and more rewarding hairy mammillarias, forgiving of most things except wet roots. Grow it in a very free-draining, mostly mineral mix in a pot only a little larger than the plant, and give it as much bright light as you can — ample sun keeps the growth tight and encourages the fullest coat of hair and the best flowering. Water thoroughly through the warm months once the soil has dried out, then ease off completely for a cool, dry winter rest, which is what triggers the spring ring of flowers.
The main hazard is overwatering, especially in cool or dull conditions; water sitting in the wool or against the base invites rot. When watering, aim for the soil rather than over the crown, and let the plant dry quickly afterwards. See Watering and Repotting for general technique.
Propagation
Seed is the primary method and germinates readily on a warm, gritty surface kept humid until the seedlings establish — see Propagation — seed. Older, clustering plants also produce offsets that can be gently detached, allowed to callus for a few days, and potted into the same dry, mineral mix. Because offsets root slowly, keep them barely moist until new growth appears.
Common problems
- Rot — almost always from overwatering, a slow-draining mix, or a cold wet winter; the plant softens and discolours, usually from the base.
- Discoloured or matted hair — overhead watering and trapped debris can dirty and clump the white wool; water at soil level and keep the plant clean.
- Etiolation — too little light makes the body stretch and pale and the hair thin out, spoiling the compact, silvery look.
- Pests — mealybugs love to hide in the wool and between tubercles, and red spider mites can bronze the skin in hot, dry air. See Pests and diseases.
See also
- Mammillaria — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — offsets · Pests and diseases