Schlumbergera
Schlumbergera is a small genus of epiphytic and lithophytic cacti native to the coastal mountains of southeastern Brazil, universally grown as holiday cacti for the showy, jewel-toned flowers they throw open in the depths of winter. Unlike the spiny desert cacti most people picture, these are forest plants with soft, flattened, leaf-like stem segments that arch and cascade, making them classic hanging-basket and windowsill subjects. Cultivated forms are among the most familiar houseplants in the world, sold each year under names such as Christmas cactus, Thanksgiving cactus and the older Zygocactus.
Description
Plants in the genus Schlumbergera are made up of chains of flat, segmented stems called cladodes. Each segment is a modified stem — not a leaf — joined end to end so the whole plant grows in arching, branching sprays that eventually trail over the edge of a pot. The margins of the segments carry small notches or teeth whose shape is one of the main ways growers tell the species apart: rounded, scalloped edges point to the true Christmas cactus group, while sharp, forward-pointing "claws" mark the Thanksgiving cactus.
The flowers are the main event. They emerge from the areoles at the tips of the terminal segments and are strongly zygomorphic — that is, mirror-symmetric rather than radial — with tiers of swept-back tepals that give them a distinctive tubular, tumbling look. Colours in the wild are typically pink to magenta, but generations of breeding have added white, salmon, orange, red, gold and bicolours. Most are pollinated in habitat by hummingbirds. As short-day plants, they set their buds in response to lengthening nights and cooler temperatures, which is why they bloom so reliably around the winter holidays of the Northern Hemisphere.
Distribution and habitat
The genus is endemic to a small region of the Atlantic coastal mountains (the Serra do Mar and Serra dos Órgãos) of southeastern Brazil, chiefly in the states of Rio de Janeiro, São Paulo and Espírito Santo. There the plants grow as epiphytes perched in the forks and mossy branches of trees, or as lithophytes wedged into shaded rock crevices, usually at cool, humid, higher elevations.
This forest origin explains everything about how they like to be grown: dappled light rather than full sun, humidity, steady moisture in the growing season, and roots that are never left sitting in stagnant wet. Some wild species have become rare through habitat loss, though the plants in cultivation are almost entirely nursery-raised hybrids far removed from their wild ancestors.
Notable species
- Schlumbergera truncata — the Thanksgiving cactus or crab cactus, with sharply toothed "clawed" segments; the parent of most early-blooming hybrids.
- Schlumbergera russelliana — a true Christmas cactus species with rounded, scalloped segments; crossed with S. truncata to create the classic garden hybrids.
- Schlumbergera opuntioides — an unusual species with thicker, more paddle-like, bristly segments recalling an Opuntia.
- Schlumbergera orssichiana — noted for exceptionally large flowers and used in breeding to enlarge modern cultivars.
Many plants sold simply as "Christmas cactus" are in fact hybrids grouped under Schlumbergera × buckleyi, the classic cross between S. russelliana and S. truncata.
Cultivation
Holiday cacti are among the easiest and longest-lived flowering houseplants, and well-kept specimens are routinely passed down for decades. Grow them in bright, indirect light — an east or north window is ideal — with protection from harsh midday sun, which bleaches and reddens the segments. Because they are forest epiphytes rather than desert plants, they want a more open, humus-rich but still free-draining medium than a typical cactus; an orchid or potting mix lightened with bark and perlite suits them well.
Water more generously than you would a desert cactus, letting the top of the mix dry between waterings but never allowing the plant to bake bone-dry during active growth. Ease off in the resting period. They actively dislike soggy roots, so the pot must drain freely. See Watering and Repotting for general technique — and note that these plants often flower best when slightly pot-bound, so resist over-potting.
The key to reliable bloom is triggering bud set. As short-day plants, they initiate flowers when nights grow long and temperatures cool. In autumn, give them around six weeks of cool nights and long, uninterrupted darkness (a spare room or unheated porch works well), keeping them away from artificial light and warm drafts. Once buds have formed, avoid moving or turning the plant, as sudden changes in light or temperature are the usual cause of bud drop. They are frost-tender and should be kept above freezing.
Propagation
Holiday cacti are very easily propagated from stem cuttings, which is how favourite plants are shared between growers. Twist or snip off a piece two or three segments long, let the cut end callous for a day or two, then set it upright in a lightly moist, gritty mix; it will root readily in warmth. See Propagation — cuttings for a full walkthrough. Named cultivars are always increased this way so they come true, whereas seed (which requires cross-pollination and produces variable seedlings) is mainly the province of hybridisers developing new colours. See Propagation — seed if you want to try raising your own crosses.
Cultivars and hybrids
Almost every holiday cactus in commerce is a hybrid rather than a wild species, bred for flower colour, form and bloom timing. Growers loosely sort them by season:
- Thanksgiving cactus — earlier-blooming hybrids derived mainly from Schlumbergera truncata, with sharply clawed segments; this is the type most often sold, despite usually being labelled "Christmas cactus".
- Christmas cactus — the classic × buckleyi hybrids with rounded segments and slightly later, pendulous blooms.
- Easter cactus — often confused with the above, but this is a separate genus, Rhipsalidopsis (syn. Hatiora), which blooms in spring and has star-shaped, radially symmetric flowers.
Modern named cultivars span the full colour range from pure white through gold, salmon and scarlet to deep magenta, including many bicolours.
Common problems
- Bud drop — the classic complaint; buds form and then fall before opening, usually after the plant is moved, turned, over- or under-watered, or exposed to a warm draft during budding. Keep conditions steady once buds appear.
- Failure to flower — almost always too much light at night or too warm in autumn; the plant needs long, cool, dark nights to set buds.
- Rot and limp segments — from waterlogged, poorly drained mix; segments go soft, dull and shrivelled from the base.
- Pests — mealybugs (white fluff in the segment joints), and occasionally scale or fungus gnats in overly wet mix. See Pests and diseases.
See also
- Schlumbergera truncata · Schlumbergera russelliana — the main parent species
- Rhipsalidopsis — the "Easter cactus", a related holiday-blooming forest cactus
- Propagation — cuttings · Soil and potting mix · Watering · Repotting · Pests and diseases