Discocactus zehntneri
| Light | Bright light with light shade from harsh afternoon sun |
|---|---|
| Water | Regularly in warm growth; keep dry and warm in winter — dislikes cold combined with wet |
| Soil | Very free-draining mineral mix (see Soil and potting mix) |
| Temperature | Warmth-loving; keep well above freezing, ideally no cooler than about 10 °C in winter |
| Propagation | Seed (primary); grafting to speed up slow seedlings |
| Toxicity | Not considered toxic to cats or dogs |
Discocactus zehntneri is a small, globular cactus from northeastern Brazil, densely cloaked in fine, interlacing whitish spines that press close to the body and give it a soft, netted appearance. At maturity it crowns itself with a woolly, bristly cephalium from which large, fragrant white flowers open at night. It belongs to the genus Discocactus, a group of flattened Brazilian cacti prized by collectors and closely protected in the wild.
Description
Discocactus zehntneri forms a low, depressed-globular body, typically flattened on top and only a few centimetres to around 10 cm across, sometimes clustering with age. The ribs are low and broken into rounded tubercles, and from each areole spring numerous slender spines — whitish to pale grey, often curving and interlacing over the surface so that the green body is partly veiled beneath them. The form once known as Discocactus araneispinus is distinguished by especially fine, spidery, tightly appressed spines, and is now generally treated as part of this species.
As the plant reaches flowering size it develops a cephalium at the crown: a dense patch of wool and bristles from which the flowers emerge. The blooms are white and slender-tubed, opening in the evening and releasing a strong sweet fragrance to attract night-flying pollinators; each lasts only a night or two.
Distribution and habitat
The species is native to the Brazilian states of Bahia and neighbouring areas of the northeastern sertão, where it grows in hot, seasonally dry country. Plants root in gritty, quartz-rich or sandy soils, often among rock and low scrub, tucked into positions that give a little shade and quick drainage. The climate is one of pronounced wet and dry seasons — warm and humid during the rains, then long and dry — a rhythm worth keeping in mind in cultivation.
Like others in the genus, wild populations are localised and vulnerable to habitat loss and over-collection.
Cultivation
Discocactus zehntneri is a rewarding but somewhat demanding plant, and the two things it most resents are cold and stagnant moisture. Grow it warm and bright, with light shade from the fiercest afternoon sun, in a very free-draining, largely mineral mix. Water generously through the warm growing season once the soil has dried, then reduce sharply as temperatures fall; through winter keep it dry and, above all, warm. Cold wet roots are the classic cause of loss.
Because the species is naturally slow and can be touchy on its own roots, many growers raise or maintain plants by grafting, which speeds growth and sidesteps rot in young seedlings. See Watering and Repotting for general technique.
Propagation
Seed is the standard and most reliable method. The fine seed is sown on a warm, moist mineral surface and germinated with humidity and warmth; seedlings are small and slow, which is why grafting onto a vigorous rootstock is a popular way to bring them on. The species clusters only modestly, so offset division is a minor route at best. See Propagation — seed, and for grafted material Grafting.
Common problems
- Rot — by far the commonest cause of death, from cold combined with wet or from a slow-draining mix; the body softens and discolours, often from the base.
- Chill damage — this is a warmth-loving species; prolonged cold, even when dry, can scar or weaken it.
- Slow, stalled growth — usually too little warmth or light; grafting is the standard remedy for reluctant seedlings.
- Pests — mealybugs (white fluff in the areoles and cephalium) and red spider mites (fine webbing, bronzed skin) are the usual offenders. See Pests and diseases.
Legal status
The genus Discocactus is listed on CITES Appendix I, the most restrictive category, which sharply limits international trade in wild-collected specimens. Nursery-propagated plants can be traded legally under the appropriate documentation, but wild collection and cross-border movement of habitat plants is tightly controlled. Growers acquiring or moving plants internationally should ensure they come from a reputable source with the correct paperwork. Collecting from the wild is not appropriate.
See also
- Discocactus — the genus overview
- Grafting · Soil and potting mix · Watering · Propagation — seed · Pests and diseases
- CITES