Oreocereus trollii
| Light | Bright light to full sun; loves all the direct light it can get |
|---|---|
| Water | Moderate in the growing season; let the mix dry between waterings, keep dry in winter |
| Soil | Very gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Tolerates cold if dry; hardy in USDA zones 9a–11, briefly lower when bone dry |
| Propagation | Seed; offsets and stem cuttings |
| Toxicity | Non-toxic to cats and dogs |
Oreocereus trollii is a compact, slow-growing columnar cactus from the high Andes of Bolivia and northern Argentina, and one of the most heavily woolly members of its genus. Its short green columns are wrapped in long, silky white hairs that all but hide the body and the reddish spines beneath, an adaptation to fierce mountain sun and cold that also makes it one of the most ornamental of the "old man" cacti. It is commonly known as the old man of the Andes, a name it shares with its relatives in Oreocereus.
Description
Oreocereus trollii forms squat, upright columns that usually stay under a metre tall and branch or offset from the base to build a low clump over time. The stems are relatively thick for their height and carry numerous low ribs lined with closely set areoles. From each areole grows a dense veil of long, wavy white hair, so profuse that a well-grown plant looks like it has been draped in cotton wool.
Pushing through the wool are stiff spines, typically yellowish to reddish-brown, with the central spines longer and more prominent than the radials. Mature plants produce funnel-shaped flowers near the stem tips in shades of pink to purplish-red, borne through the warmer months. The hair is not merely decorative: in habitat it shades the body from intense high-altitude sun and helps buffer the plant against night-time cold.
Distribution and habitat
The species grows at high elevation in the Andes of Bolivia and northern Argentina, on rocky slopes and among grasses where drainage is sharp and the air is thin, bright and cold. Plants there endure strong sun, wide swings between day and night temperatures, and a distinctly dry, chilly winter. Understanding these origins is the key to keeping the species happy in cultivation.
Cultivation
Oreocereus trollii is a rewarding grower that rots easily if treated like a soft, warm-climate cactus, so the aim is to recreate its bright, airy, mineral home. Grow it in a very gritty, free-draining mix with plenty of coarse material, and give it as much direct light as you can — strong sun keeps the wool dense and white, whereas too little light thins the hair and makes the columns stretch.
Water moderately while the plant is in active growth, letting the mix dry out between waterings, and then keep it essentially dry through winter. A cold, dry winter rest is well tolerated and helps encourage flowering; the danger is not cold itself but the combination of cold and wet. Good air movement keeps the wool clean and discourages rot. See Watering and Repotting for general technique.
Propagation
The species is usually raised from seed, sown on a gritty surface and kept warm and humid until the seedlings establish; growth is slow but steady. Because mature plants form clumps, established offsets can also be removed and rooted, and stem sections can be taken as cuttings — in both cases, let the cut surface callus well before setting the piece on barely moist mineral mix. See Propagation — offsets for handling clumping plants.
Common problems
- Rot — the main killer, almost always from a wet, cold or poorly draining mix; the base or a stem softens and discolours.
- Etiolation — too little light makes the columns thin, pale and sparsely haired, losing the plant's signature woolly look.
- Dirty or matted wool — dust, algae and overhead watering can grey the hairs; careful watering and good airflow keep them clean.
- Pests — mealybugs love to hide in the wool where they are easily overlooked, and red spider mites may attack in hot, dry, stagnant air. See Pests and diseases.
See also
- Oreocereus — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Repotting