Mammillaria compressa
| Light | Bright light with some direct sun; tolerates a little afternoon shade |
|---|---|
| Water | Moderately in growth; allow to dry fully between waterings, keep dry in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Offsets (primary); seed |
| Toxicity | Non-toxic to cats and dogs |
Mammillaria compressa is a vigorous, freely clustering cactus from central Mexico that in time builds up into broad mounds of many heads. Each stem is packed with angular, keeled tubercles bearing conspicuous white wool and bristles in the axils, and rings of small purplish-pink flowers open around the crown in spring — a display so reliable across its many offsets that the plant has earned the common name mother of hundreds.
Description
Mammillaria compressa begins as a solitary head but soon offsets from the base and sides, eventually forming a dense clump that can spread to 30 cm or more across and mound upward over many years. Individual stems are cylindrical, blue-green to grey-green, and made up of firm, angular tubercles that are bluntly keeled and closely set.
The axils between the tubercles are filled with persistent white wool and one or more long, twisting bristles, so the whole plant often looks bearded. Spines are few, stiff and unequal — usually four to six chalky-white radials with brownish tips and no central spine — fading to grey with age. In late winter and spring the plant produces a neat ring of small, bell-shaped flowers near the crown of each mature head, purplish-pink to magenta, followed by slender red seed pods that push up out of the wool.
Distribution and habitat
The species is native to the arid highlands of central Mexico, where it grows in states such as Hidalgo, Querétaro, San Luis Potosí and Guanajuato. It grows on rocky slopes in arid scrub and semi-desert at roughly 1,000–2,240 m, often growing among rocks that give the roots sharp drainage and the clumps a little shelter. It is a widespread and variable species, and several forms and varieties have been described across its range.
Cultivation
Mammillaria compressa is one of the easier and more forgiving Mammillaria for a collection, which makes it a good choice for newer growers. Give it a very free-draining, mostly mineral mix and the brightest spot you can offer; good light keeps the clump compact and encourages flowering, while too little light makes the heads stretch and pale. A slightly larger pot is useful once clustering gets going, since the plant is a strong grower and appreciates the room.
Water thoroughly during the warm months once the soil has dried out, then let it dry again before the next watering. Keep the plant dry and cool through winter — this winter rest both prevents rot and sets up the spring ring of flowers. Extra grit in the mix suits it, but is not essential. See Watering and Repotting for general technique.
Propagation
The simplest method is division of the clump: mature offsets can be detached, the cut surface allowed to callus for a few days, and then potted into a gritty mix to root. Because the species clusters so freely, offsets are usually plentiful. It also grows readily from seed sown on a warm, mineral surface kept humid, which is the best route if you want many plants or a particular provenance. See Propagation — offsets and Propagation — seed.
Common problems
- Rot — the usual cause of loss, almost always from overwatering, a slow-draining mix, or moisture sitting in the clump over winter; heads soften and discolour from the base.
- Etiolation — too little light makes the stems stretch, pale and lose their tight, tuberculate look.
- Pests — mealybugs love to hide in the woolly axils, and root mealybugs can lurk unseen at the roots; red spider mites may bronze the skin in hot, dry conditions. See Pests and diseases.
See also
- Mammillaria — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — offsets · Propagation — seed
- Pests and diseases