Mammillaria rhodantha
| Light | Bright light with some direct sun; can take more sun than many small cacti |
|---|---|
| Water | Moderate in the growing season, allowing the mix to dry between waterings; keep dry and cool in winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Best from seed; older, dichotomously branched plants can be divided (see Propagation — offsets) |
| Toxicity | Non-toxic to cats and dogs; spines are the only hazard |
Mammillaria rhodantha is a cylindrical cactus from central Mexico, grown for its densely spined stems and its neat crown of deep pinkish-red flowers. The spines vary enormously in colour from plant to plant — running through white, yellow, amber, red and brown — which has earned it the common name rainbow pincushion. It is one of the easier and more forgiving members of the large genus Mammillaria, and a good choice for a beginner.
Description
Mammillaria rhodantha forms an erect, cylindrical stem that lengthens with age. Plants are typically solitary when young, but with age the growing point often divides dichotomously — splitting in two, and repeating — to build up a small clump or cluster of heads rather than producing offsets from the base. The body is covered in spirally arranged tubercles, each tipped with an areole bearing a dense mix of shorter radial spines and a few longer, stouter central spines. It is this spination that gives the species much of its appeal: the colour is highly variable between individuals and populations, so no two clones look quite alike, and several named forms and subspecies have been distinguished on the basis of spine colour and density.
Like most Mammillaria, it flowers in a ring around the top of the stem. The blooms are small, funnel-shaped and a rich pinkish-red to magenta, appearing over a long season and often followed by slender pinkish fruit that push out from between the tubercles, carrying orange-brown seeds.
Distribution and habitat
The species is native to the highlands of central Mexico, where it grows on rocky slopes, in oak and pine woodland, and among volcanic outcrops at moderate to high elevation. In habitat it often grows in the shelter of rocks and low vegetation, rooted in shallow, well-drained mineral soil. Its montane origin means it is accustomed to bright light, cool nights and a distinctly dry season.
Cultivation
Mammillaria rhodantha is undemanding by cactus standards and tolerates a range of conditions, which makes it well suited to beginners. Grow it in a gritty, free-draining mineral mix and give it bright light with some direct sun — good light keeps the spination dense and well coloured, while too little light produces weak, drawn growth.
Water moderately through the warm growing months, letting the mix dry out between waterings, and then keep the plant dry and cool through winter. A cold, dry rest not only prevents rot but also encourages the crown of flowers the following season. As with most cacti, overwatering — especially in a heavy mix or during cold weather — is the main thing to avoid. See Watering and Repotting for general technique.
Propagation
This species is grown mainly from seed, which is also the best route if you want to see the full range of spine colours segregate out; seed is sown on a warm, gritty surface and kept humid until the seedlings establish. Unlike the freely-offsetting pincushions, M. rhodantha does not pup from the base — it builds up multiple heads by dividing dichotomously as it ages — so vegetative propagation means cutting apart an older, branched plant rather than detaching basal offsets. Let any cut surface callus before potting up; see Propagation — offsets.
Common problems
- Rot — usually the result of overwatering or a poorly draining mix, particularly in winter; stems soften and discolour from the base.
- Etiolation — too little light causes pale, elongated growth and sparse, weak spines instead of the compact, well-spined habit.
- Pests — mealybugs (white fluff among the tubercles and on the roots) and red spider mites are the usual offenders; see Pests and diseases.
See also
- Mammillaria — the genus overview
- Soil and potting mix · Watering · Propagation — offsets · Propagation — seed · Repotting · Pests and diseases