Cumulopuntia rossiana
| Light | Full sun to very bright light |
|---|---|
| Water | Sparingly in growth; keep completely dry and cold in winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Hardy to hard frost if kept bone dry; roughly USDA zone 8 and warmer |
| Propagation | Offsets (segments); seed |
| Toxicity | Not known to be toxic to cats or dogs, but the spines and glochids are hazardous |
Cumulopuntia rossiana is a small, low-growing, clumping opuntioid cactus from the high Andes of Bolivia and Argentina, prized by collectors for its cheerful, disproportionately large flowers in shades of bright orange, red and yellow. Its short, knobbly segmented stems form tight cushions or low mounds close to the ground, an adaptation to the cold, windswept mountain grasslands where it grows.
Description
Cumulopuntia rossiana builds up as a low clump or cushion of short, egg- to club-shaped segments, each usually only a few centimetres long. Like other opuntioids it carries two kinds of armament: the visible spines, which are stiff and can be pale to brownish, and the tiny barbed glochids clustered at each areole that detach at the lightest touch and lodge painfully in skin. The joints root readily where they touch soil, so a plant slowly spreads outward into a broader mat over the years.
The flowers are the main attraction and are large relative to the small body, opening in shades from bright orange through red to yellow, sometimes with subtle bicolour tones. They appear in the warmer months and open in bright sun. The species is variable across its range, and plants offered under this name (and under synonyms such as Tephrocactus rossianus and Austrocylindropuntia rossiana) can differ noticeably in segment shape, spination and flower colour.
Distribution and habitat
The species is native to the high Andes of southern Bolivia and northwestern Argentina, where it grows at considerable altitude in open, stony grassland and among rocks. These are harsh, high-elevation habitats: strong sun, sharp drainage, wide swings between warm days and freezing nights, and a pronounced dry season. The low, ground-hugging growth form helps the plant shelter from wind and cold and take advantage of warmth radiating from the surrounding rocks and soil.
Cultivation
Grow Cumulopuntia rossiana hard and dry. It wants the brightest position you can give it — full sun outdoors or the sunniest spot under glass — in a very gritty, mostly mineral mix that drains almost instantly. Water moderately through the warm growing season once the soil has dried, then withhold water completely from autumn onward.
As a high-altitude plant it tolerates real cold, and many growers keep it frost-hardy well below freezing, but only if it is kept absolutely dry through winter; the combination of cold and damp is what rots it. Its natural toughness makes it a good candidate for an unheated greenhouse, a cold frame or an outdoor rock garden in a suitably dry-winter climate. See Watering and Repotting for general technique, and handle the plant with care — the glochids are far more of a nuisance than the spines.
Propagation
The easiest method is vegetative. Detached segments root readily: remove a joint, let the cut surface callus for a few days, then set it on a gritty, barely moist mix until roots form. Because the clump is made of loosely attached segments, offsets are usually available without harming the parent. See Propagation — offsets and Propagation — cuttings.
Seed is also possible and is the way to capture the species' natural variation, though germination of high-Andean opuntioids can be slow and erratic. See Propagation — seed.
Common problems
- Rot — the main killer, caused by too much water, a slow-draining mix, or cold combined with damp in winter. Keep it lean and dry.
- Etiolation — too little light makes the segments soft, elongated and pale, and discourages flowering; give it as much sun as possible.
- Glochids — not a plant problem but a grower one: the barbed bristles detach at a touch, so repot with tongs, thick gloves or folded paper.
- Pests — mealybugs (white fluff in the areoles and around the roots) and red spider mites are the usual offenders. See Pests and diseases.
See also
- Cumulopuntia — the genus overview
- Opuntia and other opuntioid cacti
- Soil and potting mix · Watering · Propagation — offsets · Propagation — cuttings · Propagation — seed · Repotting · Pests and diseases