Schlumbergera truncata
| Light | Bright, filtered light; protect from harsh direct summer sun |
|---|---|
| Water | Regularly in growth; let the top of the mix dry between waterings; slightly drier and cooler rest before bud-set |
| Soil | Open, humus-rich but free-draining mix (see Soil and potting mix) |
| Temperature | Warm through the year; a cool spell in autumn triggers flowering; keep above freezing |
| Propagation | Stem-segment cuttings (very easy); seed for breeding |
| Toxicity | Non-toxic to cats and dogs |
Schlumbergera truncata is an epiphytic, forest-dwelling cactus from the coastal mountains of southeastern Brazil, best known in cultivation as the Thanksgiving cactus or crab cactus. It is easily told apart from its close relatives by its flattened stem segments, whose margins are edged with sharply pointed, forward-hooked teeth, and it is the principal parent behind most modern holiday-cactus hybrids. See the Schlumbergera genus page for an overview of these plants and their bloom seasons.
Description
Schlumbergera truncata is a small, much-branched cactus that grows as an epiphyte or lithophyte, its arching stems built from a chain of flattened, leaf-like segments (technically cladodes). Each segment is a few centimetres long, glossy green, and edged with two to four pointed teeth per side that curve toward the tip — the feature that gives the plant its "crab" and "claw" nicknames and separates it at a glance from the rounder-toothed Christmas cactus.
The flowers appear from the segment tips in autumn, before the true winter bloom of its relatives. They are strongly zygomorphic (bilaterally symmetrical), tubular and swept back, with a protruding cluster of stamens and a style. Wild plants are typically magenta to pink, but cultivated forms span white, cream, salmon, orange, red and purple. In habitat the flowers are pollinated by hummingbirds, and — as in cacti generally — the flattened segments carry out photosynthesis in place of the leaves the plant has dispensed with.
Distribution and habitat
The species is native to the Serra dos Órgãos and surrounding coastal mountains of Rio de Janeiro state in southeastern Brazil, where it grows in humid Atlantic forest. Rather than rooting in the ground, it perches in the forks and mossy bark of trees (as an epiphyte) or on shaded rock faces (as a lithophyte), in dappled light with high humidity and roots that are never waterlogged.
Understanding this origin explains almost everything about its care: it is a shade-loving forest plant with a taste for moisture and airflow, not a sun-baked desert cactus.
Cultivation
Schlumbergera truncata is one of the most forgiving cacti for indoor growing, which accounts for its long popularity as a houseplant. Give it bright but filtered light — an east- or north-facing window, or dappled shade outdoors in summer — and an open, humus-rich mix that drains freely. Water more generously than you would a desert cactus, letting the top of the mix dry between waterings, and never let it stand in water.
The key to good flowering is the autumn trigger. As nights lengthen and cool, the plant responds to shorter days and cooler temperatures by setting buds; a spell of cool nights with long, uninterrupted darkness reliably brings on a display. Once buds form, avoid moving or rotating the plant, as sudden changes in light or temperature commonly cause bud drop. A dilute feed through the growing season and a slightly leaner, cooler rest before bud-set both help. See Watering and Repotting for general technique; plants flower best when a little pot-bound.
Propagation
Propagation could hardly be simpler. Twist off a section of two or three healthy segments, let the cut end callus for a day or two, and set it upright in a barely moist, gritty mix; it will root within a few weeks. This is the standard way to increase named plants and to share them, and it is the reason old cultivars pass down through families for generations. See Propagation — cuttings for a full walkthrough. Seed is used only in deliberate breeding, since seedlings will not come true to the parent.
Cultivars
Most plants sold as "Thanksgiving cactus" or "crab cactus" are named cultivars or hybrids derived largely from S. truncata, selected for flower colour and form across white, pink, salmon, orange, red and purple. Many commercial "holiday cactus" hybrids are crosses between S. truncata and the related Christmas cactus, combining the toothed segments of one parent with the bloom timing of the other. See the Schlumbergera genus page for the cultivar and hybrid groups.
Common problems
- Bud drop — the most common complaint; usually from moving the plant, draughts, sudden temperature swings, or letting it dry out while in bud.
- Failure to flower — too much artificial light at night or too warm an autumn prevents bud-set; give cool nights and long, unbroken darkness.
- Rot — soft, mushy segments or a collapsing base, almost always from overwatering or a poorly draining mix.
- Pests — mealybugs (white fluff in the segment joints) and, in dry air, spider mites; see Pests and diseases.
See also
- Schlumbergera — the genus overview
- Propagation — cuttings · Soil and potting mix · Watering · Repotting · Pests and diseases