Houseplant · Cactaceae
San Pedro Cactus
Echinopsis pachanoi
Give it full sun and a long dry spell between waterings, and this tall columnar cactus climbs fast for years.
Full sun
Every 10–21 days
50–95°F · 10–35°C
USDA 8–11
Overview
San Pedro is a tall, columnar cactus from the Andes of Ecuador and Peru, where it grows on rocky mountain slopes. Indoors it makes a striking, low-fuss specimen, sending up ribbed green columns that can reach well over head height in time. It earns its keep on a sunny windowsill and asks for very little once you get the watering right.
What sets it apart from a desert cactus is how fast it moves. Given full sun and warm weather, the fast-growing stems pack on noticeable height each season, and mature plants open large, fragrant white flowers at night in summer. The clones in wide circulation, like the cultivar known simply as 'PC', grow especially quickly.
The plant carries mescaline and related alkaloids in its flesh, which is why it has a long history in traditional Andean use and why the law treats it with care. Growing it as an ornamental is fine in most places, but the flesh is not something to eat. Treat it as a houseplant to look at, not to sample.
Care
The short version: as much direct sun as you can give it, a gritty fast-draining mix, and a thorough soak only once the soil has dried out completely. Keep it warm, ease back hard on water through winter, and it nearly grows itself.
Light
Give it full sun wherever you can, ideally the brightest window in the house. It will get by in bright indirect light or partial sun, but skimp on light and the new growth comes in thin and stretched. Indoors a grow light run for 14 to 16 hours a day keeps it sturdy.
Water
Soak it thoroughly so water runs out the bottom, then wait until the mix is bone dry before watering again, usually every 10 to 21 days in the growing season. Through winter, keep it nearly dry and water only rarely. Overwatering is the single fastest way to lose this plant to rot.
Soil
Plant it in a gritty, fast-draining cactus mix, something like one part potting soil to one part coarse sand. A pH anywhere from 6.0 to 7.5 suits it. The key is that water drains straight through and never lingers around the roots.
Temperature
It's comfortable across a wide band, from 50°F to 95°F (10°C to 35°C). Warmth drives the fast summer growth, while cold, damp conditions invite rot, so bring it in or keep it dry well before the temperature drops.
Humidity
Low humidity is exactly what it wants, in the range of 10% to 40%. Ordinary dry indoor air suits it perfectly, and there's no need to mist or fuss over moisture in the air.
Feeding
Feed lightly from late spring through summer, using a phosphorus-rich houseplant fertilizer cut to half strength. Once or twice over the season is plenty. Too much nitrogen pushes soft, weak growth that's prone to stretching.
Pruning
Pruning isn't something this cactus needs. Step in only to remove damaged or rotting segments, cutting with a clean blade and letting the wound callus over before it meets any moisture again.
Repotting
Move it into a fresh pot every 2 to 4 years, or sooner if roots push through the drainage holes, the plant turns top-heavy, or the mix dries out unusually fast. Repot into dry gritty mix and hold off on watering for a week so any disturbed roots can heal.
Size & spacing
Indoors and out it can climb from 6.5 to nearly 6.5 to 19.5 feet (2 to 6 m) tall over many years, spreading 1 to 6 feet (30 to 180 cm) wide as it branches and offsets. Give a mature plant room and a stable pot, since the tall columns get heavy.
Troubleshooting
Nearly every problem with this cactus traces back to water or light. Rot from a soggy pot is the one that kills, while stretched or scorched growth just tells you the light is wrong. Match what you see below and act before soft tissue spreads.
Soft, mushy patches turning brown or black on the stem
This is rot, and it almost always starts with too much water sitting around the roots. Cold, soggy mix lets fungus and bacteria slip in through any small wound, and the soft tissue spreads from there. Cut back to firm green flesh with a sterile blade, let the wound dry and callus, then re-root the healthy top in dry, gritty mix.
Fix:
- Cut away all soft and discolored tissue back to firm green flesh with a sterile blade
- Let the cut surface callus in a dry, airy, shaded spot for 1-2 weeks
- Re-root the healthy upper section in dry, gritty mix
- Withhold water until new roots form
Thin, pale new growth stretching toward the window
This is etiolation, the plant reaching for light it isn't getting enough of. The fresh growth comes in skinny and pale next to the older ribbed sections, and it bends toward the brightest spot in the room. Move it into full sun, but ease it over a couple of weeks so it doesn't scorch, and cut back on feeding while it recovers.
Fix:
- Move to the brightest available spot or full sun
- Acclimate gradually over 2-3 weeks to avoid sunburn
- Reduce or stop fertilizing
Bleached tan patches on the side facing the sun
This is sunburn, and it shows up when a plant grown in shade meets harsh direct sun all at once. The scorched patches sit only on the sun-facing side and won't soften or spread the way rot does. Shift it to a bright but lightly shaded spot, then reintroduce full sun slowly over two to three weeks.
Fix:
- Move to a bright but lightly shaded position
- Reintroduce to full sun gradually over 2-3 weeks
Toxicity
This cactus is not a plant to eat. The flesh holds mescaline and related alkaloids, so chewing any part can cause vomiting and neurological effects in pets, livestock, and people alike. The stiff spines are a second hazard, ready to puncture a curious mouth, paw, or hand, so site the plant out of reach of children and animals.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Caution
The ASPCA doesn't list the genus as orally poisonous, but the flesh carries mescaline and related alkaloids, so a cat that chews on it may drool, vomit, or act jittery and out of sorts. The sharp spines are the more immediate danger, since they puncture a curious mouth or paw with ease. Best kept out of reach.
Dogs Caution
A dog that gnaws a stem can take in the same alkaloids and end up with stomach upset, vomiting, or unsteady, disoriented behavior. The stiff spines also tear at the mouth and gums. Most dogs leave it alone, but the determined chewer is the one to watch.
Horses Caution
There's no record of horses being poisoned, yet the mescaline-bearing flesh would unsettle the gut and could leave a horse dull or unsteady if it ate enough. The spines alone make it a poor thing to have near a paddock.
Rabbits Caution
A rabbit is small enough that even a little of the alkaloid-rich flesh could bring on digestive trouble and odd, sluggish behavior, so it's not a safe nibble. Keep the pot well away from any free-roaming bunny.
Livestock Caution
Grazing animals such as goats, sheep, and cattle could swallow the alkaloids along with the flesh and show signs of an upset stomach or dull, off-balance behavior. Fence the plant off from anywhere stock can reach.
Birds Caution
Little is documented for birds, but the same alkaloids that affect mammals make a pecked stem a poor idea, and the spines can hurt a probing beak. Treat it as off-limits for pet birds.
People Caution
The flesh contains mescaline, a psychoactive alkaloid, so eating any part can cause vomiting and neurological effects and is not safe. Children are also at risk of painful spine punctures. Grow it as an ornamental and keep it out of reach.
Wear thick gloves and lift larger plants with folded newspaper or foam padding; the rigid spines readily puncture skin. Keep within reach limited for children and pets to avoid spine injuries.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Most San Pedro you'll meet is the standard species, but a couple of named forms turn up in collections. These are the two worth knowing.
'Monstrose' (San Pedro Monstrose)
A mutation gives it lumpy, knobby, irregular growth with few or no spines, and it's grown purely as an ornamental novelty.
'PC' (Predominant Cultivar)
This is the most widely circulated clone in the US, prized for vigorous, fast growth and short spines.
How to propagate
San Pedro is easy to multiply, and most growers skip seed entirely in favor of taking cuttings or pups from a plant they already have.
Stem cuttingsEasy
Spring to early summer · 4-8 weeks to root
Cuttings are the easy way to start more plants, taken in spring or early summer while the cactus is growing. Slice off a segment, stand it in the shade for one to two weeks until the cut surface calluses over, then set it in dry, gritty mix and water sparingly. It puts down roots in about four to eight weeks.
Offsets & pupsEasy
Spring to summer · 4-8 weeks to root
Older plants throw out pups and basal branches you can detach in spring or summer. Twist one free, let the wound callus the same way you would a cutting, and root it in dry substrate, where it takes hold in roughly four to eight weeks.
SeedModerate
Spring · Several months to a year
Seed is the slow road, sown in spring on a gritty surface and kept warm and humid until it sprouts. The seedlings creep along at first, taking anywhere from several months to a full year to establish, which is why most growers reach for cuttings instead.
Myths
San Pedro and peyote are the same cactus.
They are two different plants. Peyote is the small, button-shaped Lophophora williamsii, while San Pedro is the tall columnar Echinopsis pachanoi. Both contain mescaline, but they are not the same species.
Just growing a San Pedro cactus is illegal in the US.
Keeping the living plant as an ornamental is legal in most US states. What crosses the line is extracting or preparing mescaline from it, which is a Schedule I controlled-substance offense, and a few jurisdictions add their own limits.