The rat tail cactus (Aporocactus flagelliformis) is grown for its long, thin, densely spiny stems that trail and cascade rather than grow upright — the resemblance to a tail is exactly where the name comes from. Given enough light, a mature plant rewards you with bright pink to magenta flowers in spring, opening along the length of the stems. Its growth habit and light needs set it apart from most desert cacti, so it’s worth treating it a bit differently than you would a barrel or paddle cactus.

Where to grow it

Because the stems can grow several feet long and trail rather than stand upright, a rat tail cactus is really at its best in a hanging pot or on a high shelf where the stems can drape freely. Grown in a standard pot on a windowsill, the stems will simply spill over the edge and trail down, which works too, but a hanging basket shows the plant off properly and keeps the delicate stem tips from getting bumped or broken. See best hanging and trailing houseplants for other plants that suit the same kind of display.

Light

Give it bright light, ideally with some direct sun. It’s more tolerant of a bit of shade than a true desert cactus like a barrel or star cactus, but it still needs considerably more light than a typical houseplant to grow well and, especially, to flower — a plant kept in dim conditions may survive for years without ever blooming. An east- or west-facing window with a few hours of direct sun, or a bright south-facing spot with some protection from the most intense midday sun, both work well.

Watering

Water thoroughly, then let the top couple of inches of soil dry out before watering again — noticeably more often than you’d water a desert cactus, but still with real drying time in between. During active growth in spring and summer, that might mean watering every one to two weeks; in winter, when the plant is resting (and this rest period is actually part of what triggers spring flowering), cut back significantly and let the soil dry out more fully between waterings.

Soil and pot

This plant sits somewhere between a desert cactus and an epiphytic one in its origins, so a pure gritty desert cactus mix tends to dry out too fast and hold too little for it. A cactus and succulent mix cut with a bit of regular potting soil or compost — closer to what you’d use for a Christmas cactus or Thanksgiving cactus — gives it enough organic matter to hold a little moisture while still draining well. A hanging pot with a drainage hole is essential; without one, water pools at the bottom and the roots sit in it with no way to escape.

Humidity

Average household humidity is fine for a rat tail cactus — it doesn’t need the elevated humidity that many tropical houseplants do. That said, it won’t complain about being grouped with other plants or given occasional light misting, particularly in a dry winter home with the heat running.

Toxicity

Rat tail cactus is non-toxic to cats and dogs. The main hazard is physical rather than chemical: the stems are covered in fine, bristly spines that can be uncomfortable to brush against, so a hanging spot out of the way of regular foot traffic and curious pets is still worth choosing.

Common problems

Shriveled or limp stems usually mean underwatering, especially if the soil has been bone dry for an extended stretch. A thorough watering should firm the stems back up within a few days.

Soft, mushy, or discolored stem sections, especially near the base point to overwatering and rot. Let the soil dry out fully, check that the pot actually drains, and remove any obviously mushy sections — the rest of the plant can often be saved if you catch it early.

No flowers even though the plant looks healthy is most often a light or dormancy problem. This cactus needs a genuinely bright spot with some direct sun to bloom, and it also benefits from a cooler, drier rest period in winter — without that seasonal change, it can stay vegetatively healthy indefinitely without ever flowering.

Stem sections dropping off can happen after physical damage — trailing stems are easy to snag or brush against furniture and doorways — or occasionally from stress after a big change in light or watering. A dropped section with healthy tissue can usually be rooted as a new cutting; see how to propagate houseplants from cuttings for the general method.