How to Care for a Cactus Indoors

Cacti have a reputation as the unkillable houseplant, yet more cacti die indoors than almost anything else — nearly always from kindness. The two habits that kill them are watering on a schedule and keeping them warm and dim all winter. Get light, water, and a winter rest right, and a cactus will outlive most of your furniture.

Know which cactus you have

Most cacti sold as houseplants are desert cacti — Echinocactus (the golden barrel), Mammillaria, Opuntia (prickly pear), Cereus and their relatives. They want maximum sun and a dry winter rest. A smaller group are jungle cacti — Schlumbergera (Christmas cactus), Rhipsalis, Epiphyllum — which grow on trees in forests and prefer bright indirect light, a little more water, and higher humidity. This guide focuses on desert types; treat jungle cacti more like other tropical houseplants. If you're not sure which you own, identify it with a photo in PlantMe — the app recognises cacti among its 35,000+ plant classes and gives you the matching care plan.

Light: the sunniest spot you have

Desert cacti want the brightest position in your home — a south- or west-facing windowsill with several hours of direct sun. A cactus that isn't getting enough light doesn't sulk visibly; it etiolates, producing pale, narrow, stretched new growth at the tip that never returns to normal. Rotate the pot a quarter turn every few weeks so it grows evenly.

Tip: acclimatise a cactus gradually when moving it to a sunnier spot or outdoors for summer. Even sun-loving cacti can scorch — permanent bleached or brown patches — if they jump from a dim corner to blazing midday sun overnight.

Watering: deep but rare

The rule is simple: water thoroughly, then not again until the soil has been completely dry for several days. In practice that means roughly every two to four weeks during spring and summer, depending on pot size, sun, and temperature. Water until it runs from the drainage hole, empty the saucer, and forget about it. Shallow sips little and often are worse than useless — they keep the surface damp (inviting rot) while the deep roots stay dry.

Soil and pots

Standard potting compost holds far too much water. Use a dedicated cactus mix, or make your own: roughly half houseplant compost, half mineral grit (coarse sand, perlite, or pumice). The pot must have a drainage hole — no exceptions. Terracotta is ideal because it wicks moisture out of the soil. Repot every two to three years in spring, going up just one pot size; a snug pot dries faster and is safer than a roomy one.

The winter rest most people skip

From late autumn to early spring, desert cacti want to be cool — ideally 10–15°C — bright, and almost completely dry. A cold windowsill in a barely heated room is perfect. This dormancy is not optional decoration: it is what triggers flower buds in many species, including Mammillaria and Echinopsis. A cactus kept warm and watered year-round grows weakly, stretches, and rarely blooms.

Feeding

Feed lightly: a half-strength cactus fertiliser (low nitrogen, higher potassium) once a month from mid-spring to late summer is plenty. Never feed in winter.

Common problems

• Soft, yellowing or blackening base — rot from overwatering. Unpot immediately, cut away mushy tissue and roots, let the plant callus for a week, and repot in dry gritty mix.
• Pale, thin, stretched new growth (etiolation) — not enough light. Move it to full sun; the stretched section is permanent.
• Wrinkled, shrivelled body with bone-dry soil — thirst. One deep soak usually replumps it within days.
• Brown, corky patches from the base upwards on an old plant — corking, a natural ageing process, not a disease.
• White fluffy tufts in the spines — mealybugs. Dab with a cotton bud dipped in 70% isopropyl alcohol; check the roots too.

Warning: never water a cactus "just in case". A thirsty cactus recovers with one soak; an overwatered cactus is often already rotting inside by the time it looks sick. When in doubt, wait another week.

If your cactus looks off and you can't tell rot from thirst from sunburn, photograph it in PlantMe — the disease-diagnosis model checks it against 500+ problems and gives you a step-by-step rescue plan.