Houseplant · Cactaceae
San Pedro Cactus
Echinopsis pachanoi
Ribbed green columns rise tall and fast, tipped in summer with large, fragrant white flowers that open in the dark.
Full sun
Every 10–21 days
50–95°F · 10–35°C
USDA 8–11
Overview
San Pedro grows as a tall, ribbed green column, a cactus from the rocky Andean slopes of Ecuador and Peru. The stems rise straight and vertical, marked with lengthwise ribs from base to tip, and a mature plant climbs well past head height. Up close the flesh is firm and green, and the ribs are studded with the areoles that carry its spines.
These columns thicken and lengthen fast. New growth pushes up firm and green at the tips, while the older sections below hold their deep ribbing, and in summer a mature stem opens large, fragrant white flowers after dark. The spines vary by form, short and neat on the widely grown 'PC' clone.
Beneath that green skin the flesh holds mescaline and related alkaloids, the compounds behind its long traditional Andean use and its legal restriction. The living plant is legal to grow as an ornamental in most places, but the flesh is not edible. What you see is a plant to look at closely, not to taste.
Care
The short version: this ribbed green cactus wants strong direct sun, a gritty fast-draining mix, and a deep soak only after the soil has dried out completely. Keep it warm, water little in winter, and the firm green columns climb almost on their own.
Light
Set it in full sun, ideally the brightest window, where strong light keeps the columns thick and firm. In bright indirect light or partial sun it survives, but the new growth comes in thin and pale and stretches upward. Indoors, a grow light run 14 to 16 hours a day holds that firm, ribbed form.
Water
Water it deeply until the excess drains away, then leave the mix until it is bone dry to the touch, usually every 10 to 21 days in the growing season. In winter keep it nearly dry, watering only rarely. Standing moisture softens the roots into rot, the fastest way to lose the plant.
Soil
Root it in a gritty, fast-draining cactus mix, roughly one part potting soil to one part coarse sand, so water clears the roots at once. A pH of 6.0 to 7.5 suits it. The coarse grit keeps the mix open and never lets water pool at the base of the stem.
Temperature
It holds firm across a wide range, from 50°F to 95°F (10°C to 35°C). Warmth swells the fast summer growth at the stem tips, while cold, damp air softens the flesh into rot, so bring it in or keep it dry before the chill comes.
Humidity
Dry air suits its firm skin, with low humidity around 10% to 40% exactly right. The ordinary dry air of a room is enough, and there is no misting to bead on the ribs.
Feeding
Feed lightly from late spring through summer with a phosphorus-rich houseplant fertilizer at half strength, once or twice across the season. Heavy nitrogen swells the tissue soft and weak, and that spongy growth stretches and loses its firm ribbing.
Pruning
The green columns need almost no pruning. A clean blade takes out any damaged or rotting segment, and the raw cut is left to dry into a firm callus before it meets moisture again.
Repotting
Move it into fresh mix every 2 to 4 years, or sooner when roots poke from the drainage holes, the column turns top-heavy, or the mix dries oddly fast. Set it into dry gritty mix and leave it unwatered for a week so the cut and jostled roots seal over.
Size & spacing
In time the column stretches from 6.5 to 19.5 feet (2 to 6 m) tall and the clump spreads 1 to 6 feet (30 to 180 cm) as new stems branch and offset from the base. The tall, ribbed stems grow heavy near the top, so a mature plant needs room and a stable, weighted pot.
Troubleshooting
Most of what goes wrong shows plainly on the plant's surface. Soft, darkening flesh means rot from too much water, while pale, stretched stems or bleached patches point to a light problem. Match the look of the tissue below and act before the soft, discolored area widens.
Soft, mushy stem tissue darkening to brown or black
This is rot, seen as firm green flesh turning soft and slumping into brown or black patches. It begins where water sits around the roots, letting fungus and bacteria enter a small wound and creep up the stem. Cut back to firm green flesh with a sterile blade, let the raw face dry into a callus, then re-root the sound green 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
Pale, narrow new growth stretching toward the light
This is etiolation, where the newest growth pushes up thin and pale against the deeper green, ribbed sections below. The soft new column leans and reaches toward the brightest light in the room instead of standing straight. Move it into full sun over a couple of weeks so it does not scorch, and cut back feeding while the tip firms up.
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 sun-facing side
This is sunburn, showing as bleached yellow or tan patches on the green skin where direct sun struck a shade-grown plant. The scorched area stays only on the exposed side and keeps its firm surface, never softening or spreading the way rot does. Move it to a bright but lightly shaded spot, then bring back full sun by degrees over two to three weeks.
Fix:
- Move to a bright but lightly shaded position
- Reintroduce to full sun gradually over 2-3 weeks
Toxicity
Behind its firm green skin, the flesh carries mescaline and related alkaloids, so chewing any part can cause vomiting and neurological effects in pets, livestock, and people. The rigid spines set along the areoles are a sharp second hazard, ready to puncture a mouth, paw, or hand. Keep the plant out of reach of children and animals.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Caution
The ASPCA does not list the genus as poisonous to eat, but the firm green flesh carries mescaline and related alkaloids, so a cat that bites into it may drool, vomit, or turn jittery. The rigid spines are the sharper danger, quick to drive into a curious mouth or paw. Keep it out of reach.
Dogs Caution
A dog that gnaws through the green skin swallows the same alkaloids and can develop stomach upset, vomiting, or unsteady, disoriented behavior. The stiff spines also tear at the mouth and gums. Most dogs leave the spiny column alone, but the determined chewer bears watching.
Horses Caution
No horse poisonings are on record, yet the mescaline-bearing flesh under the green skin would unsettle the gut and could leave a horse dull or unsteady after enough of it. The rigid spines alone make it a poor thing to keep near a paddock.
Rabbits Caution
A rabbit is small enough that even a little of the alkaloid-rich green flesh could bring on digestive trouble and dull, sluggish behavior, so it is no safe nibble. Keep the spiny pot well away from any free-roaming rabbit.
Livestock Caution
Grazing animals such as goats, sheep, and cattle could swallow the alkaloids with the green flesh and show an upset stomach or dull, off-balance behavior. Fence the ribbed column off from anywhere stock can reach.
Birds Caution
Little is recorded for birds, but the same alkaloids in the flesh make a pecked stem a poor idea, and the rigid spines can hurt a probing beak. Treat it as off-limits for pet birds.
People Caution
The green flesh holds mescaline, a psychoactive alkaloid, so eating any part can cause vomiting and neurological effects and is not safe. Children also risk deep punctures from the rigid spines. Grow it to look at 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 shows the plain green columnar form, but two named variants stand out by their looks. Here is how to tell them apart.
'Monstrose' (San Pedro Monstrose)
A mutation twists its growth into lumpy, knobby, irregular forms with few or no spines, grown purely as an ornamental novelty.
'PC' (Predominant Cultivar)
Circulated more widely than any other clone across the US, it shows vigorous, fast growth and short, neat spines.
How to propagate
San Pedro is easy to multiply from its own green stems, and most growers skip seed to root a cutting or a pup taken from a plant they already have.
Stem cuttingsEasy
Spring to early summer · 4-8 weeks to root
A cutting is the simplest way to grow another, taken in spring or early summer from a firm green stem in active growth. Slice a segment free, stand it in shade for one to two weeks until the wet cut dries to a firm callus, then set it in dry, gritty mix and water sparingly. Roots break from the base in about four to eight weeks.
Offsets & pupsEasy
Spring to summer · 4-8 weeks to root
Older plants push out pups and basal branches low on the stem, ready to detach in spring or summer. Twist one away, let its wound dry to a callus as a cutting does, and root it in dry substrate, where it anchors in roughly four to eight weeks.
SeedModerate
Spring · Several months to a year
Seed is the slow way, scattered in spring on a gritty surface and kept warm and humid until tiny green seedlings emerge. Those seedlings inch upward at first and take anywhere from several months to a full year to establish, which is why cuttings are the usual choice.
Myths
San Pedro and peyote are the same cactus.
They are two different plants with very different shapes. Peyote is the small, round, button-shaped Lophophora williamsii, while San Pedro is the tall, ribbed, columnar Echinopsis pachanoi. Both contain mescaline, but they are not the same species.
Growing a San Pedro cactus is illegal in the US.
Keeping the living green plant as an ornamental is legal in most US states. The line is crossed by extracting or preparing mescaline from it, which is a Schedule I controlled-substance offense, and a few jurisdictions add their own limits.