Echinopsis: San Pedro Cactus & Torch Cacti

Echinopsis is a South American genus of around 80 species, from small globose plants to columnar trees reaching 6 m. The name confusion is taxonomic. In 1974 H. Friedrich folded the old genus Trichocereus into Echinopsis on the basis of shared flower structure, so Trichocereus became a synonym. Nurseries kept using the older name anyway: it predates the reclassification, and collectors still recognize it, so the label stuck.

The genus runs in a broad arc down South America: Ecuador, Peru, Bolivia, Argentina, Brazil, Paraguay, and Uruguay. The columnar species hold the Andean slopes between 1,000 and 3,000 m, in semi-arid shrubland and rocky grassland. Elevation sorts the two best-known torches. E. pachanoi sits high, at 2,000 to 3,000 m in the Peruvian and Ecuadorian Andes; E. peruviana takes the lower, drier ground from 1,000 to 2,500 m.

Under good conditions E. pachanoi puts on 30 to 45 cm of height a year, which ranks it among the fastest columnar cacti in cultivation. E. peruviana can run faster still, past 50 cm in a year where it gets warmth and enough water. Those numbers are for established plants, second year and on. Juveniles take their time while the roots fill in.

Echinopsis carries some of the largest flowers in the cactus family. Each bloom is funnel-shaped and up to 25 cm long, set on a hairy tube, in white, pink, red, or yellow depending on the species. The columnar former-Trichocereus species open at night and last a single day. The globose species are smaller and tend to flower by day.

Kept dry at the roots, E. pachanoi takes brief frost down to about −5 to −7°C, which puts it in USDA zones 9a to 10. The high Andes built that tolerance: cold nights, dry soil. The catch is moisture. At the same temperature, wet cold does far more damage than dry cold.

E. pachanoi reads light green, usually 5 to 8 ribs, with short spines under 2 cm, and comes from the higher, wetter Andes at 2,000 to 3,000 m. E. peruviana is the bluer of the two, with larger areoles and spines reaching 4 cm, off drier slopes at 1,000 to 2,500 m. The line blurs in cultivation, though. The two hybridize freely, so a plant sold under either name can sit somewhere between them.

As an ornamental, E. pachanoi is legal to buy, sell, and grow in the United States, the United Kingdom, Canada, Australia, and most other jurisdictions. The wrinkle is chemistry. The plant contains mescaline, which is Schedule I, but the cactus itself is not scheduled. You only cross a legal line if you set out to extract or consume the mescaline.

Give Echinopsis a fast-draining mineral mix: ordinary cactus soil cut with 30 to 50% pumice, granite grit, or lava rock. The watering is where it differs from desert cacti. The columnar former-Trichocereus species come from high-rainfall Andean country, so they take generous water through the growing season, as long as the mix drains right through within 24 hours.

Yes. San Pedro is Echinopsis pachanoi, the best-known plant in the genus. It sits alongside the Peruvian torch (Echinopsis peruviana) and the Bolivian torch (Echinopsis lageniformis), and all three used to be Trichocereus. That history is why San Pedro still shows up for sale as Trichocereus pachanoi. All are tall, fast-growing Andean columns, now filed under Echinopsis.