Gymnocalycium horstii
| Light | Bright, indirect light; some shade from harsh afternoon sun |
|---|---|
| Water | Moderate in the growing season; let the soil dry between waterings, keep dry in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Seed; occasional offsets |
| Toxicity | Non-toxic to cats and dogs |
Gymnocalycium horstii is a smooth-bodied, globular cactus from southern Brazil, admired for its unusually clean, glossy skin, its low count of broad rounded ribs, and its large, soft pink to almost white flowers. It is one of the more distinctive members of the genus Gymnocalycium, and among the easier Brazilian species to please in a collection.
Description
Gymnocalycium horstii forms a solitary, flattened-globular body that is comparatively large and smooth for the genus, with a satiny green skin. Where many Gymnocalycium carry numerous ribs, this species is defined by just a few broad, rounded ribs separated by shallow grooves, giving it a plump, softly segmented outline. The areoles are set along the ribs and bear a small number of short, pale, somewhat curved spines that lie close to the body rather than bristling outward.
The flowers are the plant's great attraction: large, wide-opening blooms in delicate shades from soft pink to nearly white, carried near the crown in the growing season. As with the rest of the genus, the flower buds and tube are naked (gymno- meaning bare, calycium the calyx), lacking the wool or bristles seen on many other cacti.
Distribution and habitat
The species is native to southern Brazil, in the state of Rio Grande do Sul, where it grows among rocks and low vegetation in a comparatively mild, seasonally moist climate. Plants of this region generally experience more ambient humidity and summer rainfall than the desert cacti of Mexico, which is worth keeping in mind when setting up their care.
Cultivation
Gymnocalycium horstii is a rewarding, forgiving grower and a good choice for someone moving beyond the most basic beginner cacti. Grow it in a free-draining, mostly mineral mix and give it bright light, but with a little shade from the fiercest afternoon sun — like many Brazilian Gymnocalycium it can scorch or turn a dull bronze if baked in full, unfiltered heat.
Because it comes from a summer-moist habitat, it tolerates and appreciates regular watering through the warm months; simply let the mix dry out between drinks so the roots never sit wet. Keep the plant dry and cool over winter to firm it up and encourage the following season's flowers. See Repotting for general technique.
Propagation
Seed is the usual and most reliable method, sown on a warm, humid mineral surface as described in Propagation — seed. Plants may occasionally produce offsets around the base, which can be removed once they have a little size and rooted as described in Propagation — offsets. Vegetative propagation is far less common than seed for this species.
Common problems
- Rot — usually from a slow-draining mix or standing water, especially in cool or dark conditions; the body softens and discolours from the base.
- Scorch and bronzing — too much direct, intense sun turns the smooth green skin a dull reddish-bronze and can leave permanent marks.
- Pests — mealybugs (white fluff in the areoles and around the roots) and red spider mites (fine webbing, dulled skin) are the usual offenders; see Pests and diseases.
See also
- Gymnocalycium — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Pests and diseases