Thelocactus heterochromus
| Light | Bright light; full sun once established, with a little protection from the harshest afternoon glare |
|---|---|
| Water | Sparingly; let the mix dry out fully between waterings, and keep dry and cool in winter |
| Soil | Very free-draining, mostly mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9–11, tolerant of brief light frost when bone dry |
| Propagation | Seed |
| Toxicity | Non-toxic to cats and dogs |
Thelocactus heterochromus is a solitary, flattened-globular cactus from north-central Mexico, prized for its variably coloured spines and its exceptionally large, purple-pink flowers with a darker throat. The spines range from pale straw and amber through pink to reddish or grey — often several colours on the same plant — which is exactly what the name heterochromus ("different-coloured") describes. It is one of the showier members of the genus Thelocactus and a firm favourite among collectors of Mexican globular cacti.
Description
Thelocactus heterochromus usually stays solitary, forming a firm, flattened globe that is typically wider than it is tall and reaches something on the order of a hand's width across. The body is a blue-green to grey-green and is divided into low, broad ribs that are broken up into distinct rounded tubercles, each tipped with a large, felted areole.
The spination is the plant's signature feature. Stout, somewhat flattened radial and central spines radiate from each areole in a shifting mix of colours — cream, yellow, amber, pink, red-brown and grey — so that no two plants look quite alike and the colours often shift as the spines age.
Flowers appear from near the crown, generally in spring, and are strikingly large for the size of the plant: broad, funnel-shaped blooms in vivid magenta to purple-pink, each with a noticeably darker centre. A well-grown plant can carry blooms nearly as wide as the body itself.
Distribution and habitat
The species is native to north-central Mexico, in the Chihuahuan Desert region across states such as Chihuahua, Durango and Zacatecas. It grows on rocky, well-drained slopes and flats in arid scrub and desert grassland, rooted in gritty mineral soils among rocks and low vegetation that give it a measure of shelter. Like all cacti, the genus is listed under CITES Appendix II, so international trade in wild-collected plants is regulated; nursery-raised specimens are widely available and are the responsible choice.
Cultivation
Thelocactus heterochromus is one of the more forgiving members of its genus and makes a rewarding plant for a grower with a little cactus experience. Give it a very free-draining, mostly mineral mix and as much bright light as you can offer — good light brings out the best spine colour and encourages flowering, though a little shade from the fiercest afternoon sun does no harm in the hottest climates.
Water thoroughly during the growing season only once the mix has dried out completely, then hold off again; the quickest way to lose one of these plants is a soggy pot. Through winter keep it dry and cool, which both prevents rot and sets the plant up to flower well in spring. See Watering and Repotting for general technique, and give the plant a snug pot rather than an oversized one.
Propagation
Since the plant almost always grows as a single head and rarely offsets, seed is the standard means of propagation. Sow onto a warm, gritty, mineral surface kept humid until the seedlings establish, then grow them on hard and bright. See Propagation — seed for a full walkthrough; because offsets are seldom produced, vegetative methods such as offsets or cuttings are rarely an option here.
Common problems
- Rot — nearly always the result of overwatering or a mix that holds too much moisture; the plant softens and discolours, usually from the base.
- Etiolation — too little light makes the body pale and pushes it into an unnaturally tall, domed shape while dulling the spine colour.
- Pests — red spider mites (fine webbing and a bronzed, scarred skin) and mealybugs (white fluff tucked into the areoles) are the usual offenders; see Pests and diseases.
See also
- Thelocactus — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Repotting · Pests and diseases