The Ancient Wonders of the San Pedro Cactus

By Tyson Curtis in Partnership with Flora Grubb Gardens

The popular cactus Echinopsis pachanoi (syn. Trichocereus pachanoi) is known by many names, most commonly ‘San Pedro.’ This cactus is fairly common, and no doubt you’ve seen it around, but if you dive deeper there’s so much to learn.

Echinopsis pachanoi grows in rocky, well-drained soil along the entire length of the Andes mountains, stretching from Argentina to Ecuador. A high altitude native (6000-9000 feet), this plant thrives in cold climates down to 15 degrees F.

Any cactus grower will tell you that a minimum temperature guideline usually means “when dry,” but not so with San Pedro! Most cactus get rainfall during their warm season, and so are likely to fail when exposed to a wet winter, even if they can tolerate much colder temps in habitat—but San Pedro, in its mountain habitat, receives ample rainfall while still enduring quite cold temperatures. This makes it one of the best candidates for a Mediterranean climate (like ours in the Bay Area). It just needs a bit of additional summer water to thrive.

The history of San Pedro is intertwined with Andean culture and traditional medicine, with archaeological evidence showing healers using the plant for religious divination as far back as 3000 years ago.

We love Echinopsis pachanoi for its ornamental uses in the garden. As a sturdy vertical design element it’s second to none, able to fit into tight spaces and growing 10-20 feet tall. A single stem will pup and branch, creating a staggered clump of fast-growing spires with a well-balanced form. Unlike other columnar cactus, San Pedro is relatively unspined, increasing its usefulness around patios and walkways, in pots and even indoors in a sunny spot.

Since these plants are native to a higher rainfall area, they will tolerate overwatering, with good drainage, making them easier to intermingle with other plantings, allowing designers to set softer plants against them for contrast. In fact these cactus prefer even watering, especially during the dryer months. About the only problem we encounter is yellowing, which happens when people relinquish water entirely, plant in heavy clay, or never fertilize. San Pedro appreciates fertilizer more than other cactus and will reward you with fast growth and vibrancy.

Maybe the most notable aspect of Echinopsis pachanoi are the huge white flowers, found in abundance on established specimens. These fragrant flowers are tubular and almost ten inches long and wide! The unusual size relates to the overly-large hummingbirds that pollinate them in the Andes, though they are also moth-pollinated. Since the pollinators are nocturnal, you’ll find that these huge white flowers open at night, making San Pedro an ideal candidate for a moon-viewing party in your new garden!