Turbinicarpus knuthianus
| Light | Bright light with a little shade from the harshest afternoon sun |
|---|---|
| Water | Sparingly; let the soil dry out completely between waterings, keep dry in winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Seed; offsets from established clusters |
| Toxicity | Non-toxic to cats and dogs |
Turbinicarpus knuthianus is a small, clustering cactus from San Luis Potosí in north-central Mexico, prized by collectors for its dense caps of slender white radial spines and its cheerful pink flowers. Long known in the hobby under the name Gymnocactus knuthianus, it is now placed in the genus Turbinicarpus, a group of miniature Mexican cacti famous for packing a great deal of charm into very little space.
Description
Turbinicarpus knuthianus begins life as a solitary, more or less globular to shortly cylindrical stem and, with age, offsets freely to build up low clustering mounds of heads. Each head is small — typically only a few centimetres across — and clothed in fine, needle-like white radial spines that press close to the body and largely hide the green surface beneath, giving established clumps a soft, silvery look.
The tubercles are arranged in neat spiralling rows, each tipped with a woolly areole. Flowers appear from near the crown, usually in spring, and are pink to pale magenta — bright and comparatively large for so small a plant, opening in sunshine over several days.
Distribution and habitat
The species is native to the state of San Luis Potosí in north-central Mexico, where it grows on rocky, arid ground among low scrub. Like many of its genus, it favours gritty, mineral substrates and sharp drainage, often tucked against rocks that offer a little shade and shelter. All cacti are protected under CITES, but — unlike most of the family, which is listed on Appendix II — the whole genus Turbinicarpus falls under the stricter Appendix I, which bars international trade in wild-collected plants. The small, slow-growing habitat plants should never be collected; nursery-propagated stock is widely and legally available.
Cultivation
As with most Turbinicarpus, the key to success is a very free-draining, mostly mineral mix and a cautious hand with the watering can. Grow it in bright light with only light protection from the fiercest midday sun, which helps keep the spination tight and the body compact rather than etiolated.
Water thoroughly only once the soil has dried out completely, then allow it to dry again before the next drink. Through winter keep the plant cool and completely dry — this dry rest both prevents rot and encourages a good spring flowering. The species is naturally slow, so resist the urge to push it with heavy feeding or frequent watering. See Watering and Repotting for general technique.
Propagation
Seed is the classic method for Turbinicarpus and gives the most plants, though it calls for patience as seedlings are tiny and grow slowly; sow onto a warm, mineral surface kept lightly humid (see Propagation — seed). Because T. knuthianus clusters readily, established clumps can also be increased by removing rooted or well-formed offsets and letting the cut surfaces callus before potting them into a gritty mix.
Common problems
- Rot — by far the commonest cause of loss, almost always from overwatering, a slow-draining mix, or water sitting in the crown; heads soften and discolour from the base.
- Etiolation — too little light makes the body swell and stretch, spacing out the tubercles and loosening the tidy spine cap.
- Pests — red spider mites and mealybugs are the usual offenders; watch for fine webbing or white fluff tucked among the dense spines (see Pests and diseases).
See also
- Turbinicarpus — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Repotting