Crown of Thorns

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It wants your sunniest window, south or west, with 6+ hours of direct sun; the more sun, the more blooms. In part shade it carries on but flowers less, and a lamp left on late at night can hold the blooms back too.

The more sun, the more flowers. In a dimmer spot it survives, but it flowers less, gets leggy and stays wet longer, which invites rot.

It needs dark nights, too: UW–Madison Extension finds that poor flowering usually comes from too much light at night, so a lamp left on late in that room can stop the blooms.

Soak it every 10-14 days in summer and every 2-4 weeks in winter, letting the mix dry all the way between. Three dry weeks barely faze it; cold, soggy soil is what rots it.

Water until it runs out the bottom, empty the saucer, and let the soil dry out between soaks, which takes 10-14 days in a sunny window. Water less often in winter, when it’s cooler: wet, cold soil is what kills it.

Gone for a while? Three weeks is fine if it’s watered the day you leave; it’s built for dry spells.

Spiny stems branch at odd angles into a dense shrub 1-2 feet tall indoors, with the leaves and blooms clustered at their tips. It takes its time getting there: the RHS gives it 10-20 years to mature.

Growth is slow. An older plant can get scraggly: in spring or summer, cut a stem back to a bud and it branches there. Use a knife rather than shears, since the sap gums up blades, and wear gloves.

Mildly irritating: chewed, the milky sap may upset the mouth and stomach of dogs and cats (Pet Poison Helpline) and kids (UC ANR). It can irritate skin and hurt eyes, so gloves help when you prune.

The milky sap irritates skin and can badly hurt eyes, so wear gloves and keep it out of eyes when cutting

Pet Poison Helpline rates it mild: drooling, loss of appetite, vomiting, or diarrhea, and minor irritation if the sap gets on skin or in the eyes.

For people, the sap is the real hazard. Chewed, it can blister the lips and mouth, and NC State Extension warns that in the eye it can damage the cornea, sometimes permanently. Keep it out of kids’ reach, wear gloves when you cut it, and wash your hands before you touch your face.

1. ASPCA: mild for dogs.
2. Pet Poison Helpline: mild for dogs.
3. ASPCA: mild for cats.
4. Pet Poison Helpline: mild for cats.
5. NC State Extension: mild for kids.

Cats and dogs: Most of the leading sources agree.

Kids: No poison-centre listing; rated from university extension sources. The extension signs beyond the gut are qualified, so they don’t count.

Comfortable at 50-80°F, and humidity as low as 10% is no bother to this Madagascar succulent. It rides out a chill to about 35°F (NC State), though not frost, and cold does the most harm when the soil is wet.

Temperature

50-80°F

Humidity

10%+

NC State lists no serious pests, though mealybugs turn up most often, like tufts of white cotton on the stems and where leaves join them. Scale, small brown bumps stuck to the plant, shows up now and then.

• Mealybugs
• Scale

Few. NC State lists no serious pests or diseases; mealybugs turn up most often, and rot comes from too much water.

Mealybugs look like tufts of white cotton on the stems and where the leaves meet them. Dab each one with a cotton swab dipped in rubbing alcohol (wear gloves around the spines), then check again next week.

Spider mites, scale, and thrips turn up now and then: fine webbing, small brown bumps, or a silvery, speckled look on the leaves. Spray the plant with water in the sink, then insecticidal soap if they come back.

Rot shows as stems going soft and dark at the base, or leaf spots after the plant stays wet. Let the pot dry right out, water less often, and cut off anything soft.

Give it a quarter turn toward the window each month and a light feed in spring and summer, and sweep up dropped leaves and bracts now and then. Gloves go on to prune once a year and to repot about every 2 years.

• Feeding spring-summer6× a year
• Quarter-turn toward window12× a year
• Sweep dropped leaves and bracts4× a year
• Prune with gloves (irritant sap)1× a year
• Repot with glovesevery 2 years

A cactus mix with extra perlite or grit, in a pot with a drainage hole. A clay pot helps the soil dry out between soaks.

Repot only when it outgrows its pot, in spring or summer while it’s growing. Wrap the stems in a folded towel to handle it, since the spines are sharp.

Food is optional: a balanced fertilizer, lightly, in spring and summer. Too much gives soft, fast growth and fewer flowers.

Red, pink, or yellow bracts, colored leaves around tiny green flowers, top its thick, gray, spiny stems from late winter into fall. A few small, satiny leaves cluster at the tips, with soil showing between the stems.