Cactus from the Rainforest: Christmas Cactus

Nov 26, 2021

Cactus from the Rainforest: Christmas Cactus

Nov 26, 2021

Imagine a mountainous and remote rainforest along the ocean coast. Whisps of fog drift through the trees as cascades of colorful flowers sweep down from plants perched high on the tree limbs. This is the Mata Atlântica or Atlantic Forest of Brazil, a biodiversity hotspot and birthplace of the Christmas cactus or Flor de maio (May flower). In the Southern Hemisphere this plant blooms in May (autumn); in the Northern Hemisphere it blooms during the winter holidays, hence its popularity as a Christmas gift.

Christmas cactus is a general name given to a small group (genus) of cacti called Schlumbergera that are native to the coastal mountains of southeastern Brazil, growing mostly in high altitude, moist forests where conditions are relatively cool, shaded and humid. In the wild, Schlumbergera are either epiphytic or lithophytic, meaning they grow either on moss-covered tree branches or in rock crevices filled with decayed leaves and other vegetation, rather than in the ground.

These plants are true members of the cactus (cactaceae) family even though they bear little resemblance to other species of cacti adapted to desert heat: they have photosynthetic stems rather than leaves and areoles rather than branches.

In spite of their cool and moist native habitat, these plants are hardy and grow well in a pot outdoors on a sheltered patio or indoors next to a window in bright, indirect light. With proper cultivation, they are also long-lived; Schlumbergera can live up to 50 years or more; many have been passed down in families as cherished heirlooms.

Surprisingly, a “Christmas cactus” can be one of three different species. Schlumbergera truncata blooms earlier, usually in November, and is more accurately called the Thanksgiving cactus. Schlumbergera x buckleyi (sometimes referred to as S. bridgesii) blooms later, often in December or January (hence “Christmas cactus”). Finally, there is Schlumbergera gaertneri (formerly classified as Hatiora gaertneri or Rhipsalidopsis gaertneri) which blooms in the spring, around Easter, and again later in the year (P. Geisel and C. Unruh, Holiday Cacti, Publication 8114, UC Regents, 2004).

The common and botanical names given to these plants can be confusing, and any of them may be labeled “Christmas cactus.” So how can you identify exactly which species you have?

If the plant is in bloom, the flowers of S. truncata are zygomorphic (bilaterally symmetrical when sliced lengthwise) held more or less horizontally or above the horizontal, and the pollen is yellow; whereas the flowers of S. x buckleyi are more regular and hang down below the horizontal, with pollen that is pink. The flowers of S. gaertneri are different from the other two species because they are radially symmetrical (actinomorphic) and open to a funnel shape, like a starburst.

If the plant is not blooming, the best way to identify which species you have is by looking at the stem segments (phylloclades) that form the plant. In S. truncata the stem segments have pointed teeth (dentate), often with two large teeth at the end of the segment, while in S. x buckleyi they are rounded, with more symmetrical teeth (crenate); in S. gaertneri the segments are very rounded with small notches along the edge at the aeroles. For helpful illustrations of all of these species, see Is it a Thanksgiving, Christmas or Easter Cactus? - World of Succulents

Indeed, some sources claim that the Thanksgiving cactus Schlubergera truncata is actually the one that is widely marketed as Christmas cactus.

A Brief History

Christmas cacti have been given as holiday gifts since the second half of the 19th century. Charles Lemaire, a French botanist, named the genus Schlumbergera in 1858, commemorating Frédéric Schlumberger, who had a collection of cacti at his chateau in France. Lemaire began with only one species in his new genus – a plant discovered in Brazil in 1837 which is now classified as Schlumbergera russelliana.

Schlumbergera truncata (Thanksgiving cactus) was cultivated in Europe starting in 1818, and S. russelliana was introduced in 1839. The two species were deliberately crossed in England, resulting in the hybrid now called Schlumbergera × buckleyi, first recorded in 1852, the true Christmas cactus. 

Schlumbergera gaertneri (Easter Cactus) was first described in 1884 as the variety gaertneri ofSchlumbergera russelliana). The name honors one of the Gaertner family, early settlers in Brazil.

These winter and spring-blooming species are three of the seven recognized species within the genus Schlumbergera. In addition, there are hundreds of modern cultivars (breeder-selected cultivated varieties) of the Christmas cactus.

Care and Feeding

Schlumbergera cacti do best in temperatures ranging from 50 to 70 degrees F, which makes them an obvious choice for a houseplant, but they can also live outside if they are sheltered from direct, intense sun, heat and frost. These rainforest plants need humidity. An indoor environment such as a kitchen with bright indirect light is perfect, or you can provide humidity by misting the plant or placing the pot on a saucer of pebbles filled with water so that the plant benefits from evaporation but doesn't sit in water. In their native habitat, these plants may get up to 17 inches of rain a month during their growing season (March to September). Although this drops to as little as 3 inches per month in the dry season, it's still enough to provide consistent moisture and humidity (Geisel & Unruh, Holiday Cacti).

Since these plants naturally grow in crevices of tree branches or rocks, they prefer to be in smaller pots with tight root space. The potting mix should be loose and fast draining; a good cactus mix that is somewhat acidic (pH 5.0 to 6.0) will work. Allow Schlumbergera to dry out partially, but not completely, between waterings. A good rule of thumb is to water when the top one to two inches of soil are dry (depending on the size of your pot). Fertilize every two to four weeks during the growing season using a well-balanced formulation such as 10-10-5. Liquid fertilizer mixed with water according to directions[JL1]  or granular slow-release formulations are equally effective. With reasonably good care, these hardy plants are generally free of pests or disease.

Blooming and Propagation

The trickiest aspect of Schlumbergera cultivation is getting them to bloom abundantly every year at holiday time. Schlumbergera are thermophotoperiodic, which means that temperature and short days (fewer hours of daylight) trigger bloom. Even with good care, they will probably bloom sparingly unless exposed to cool nighttime temperatures (50 to 55 degrees F) and 12 to 16 hours a day of total darkness starting about six to eight weeks ahead of their flowering period.

In the fall, a sheltered location outdoors will work as long as daylight is limited to 10 to 12 hours and nighttime temperatures dip into the 50's (but not much below 50 degrees). Indoors, a cool room where lights are not turned on at night is ideal; another option is to place the plant under a black cloth or in a closet to ensure total darkness from 5 pm to 8 am.

When flower buds are set, keep the plant away from heater vents, fireplaces and other sources of hot air; continuous warm temperatures, especially above 80 degrees, can cause the flower buds to drop. Once the plant is blooming, make sure it is regularly watered, but do not fertilize.

Schlumbergera usually remain in flower for four to six weeks and then enter a rest period, followed by a new growth cycle. After blooming is a good time to prune and shape the plant. You can use the pruned sections to easily start new plants. Allow the cut ends to dry (callus) for a few days, and then insert them about 1 inch deep in moist, clean potting mix (5 cuttings in a 6-inch pot). Use of a rooting hormone is usually not needed. Cover the pot or tray with a clear plastic bag to create a more humid environment, making sure the bag is held up and away from the cuttings.

Although far from their native rainforest home, exotic Schlumbergera cacti still brighten our winter holidays with the gift of spectacular color and beauty.

Other References

Finigan, Monica. A Tale of Two Cacti, UC Master Gardeners of Napa County, Regents of the University of California, Division of Agriculture and Natural Resources. December 9, 2015.

Hartin, Janet. “Was that Gift Really a Christmas Cactus…or Something Else?Environmental Horticulture News, Regents of the University of California, Division of Agriculture and Natural Resources, 2021.

Perry, Ed. “The Christmas Cactus,” The Stanislaus Sprout, Regents of the University of California, Division of Agriculture and Natural Resources, December 14, 2020.

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