15 November 2005
Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580 fax: 434.872.4578
A favorite gift plant at this time of year is the Christmas or Thanksgiving cactus. Many folks keep them long after receiving them as they will rebloom with proper care. Their bright pink, white, red, or violet blooms offset by the dark green succulent foliage make for a very attractive houseplant.
The Christmas cactus, Schlumbergera bridgesii, is an epiphytic plant native to a small region in the Organ Mountains north of Rio de Janeiro, Brazil in South America. Schlumbergera bridgesii grows at mountain altitudes in excess of 5000 feet in cool, dry wooded areas. Under natural conditions, Schlumbergera bridgesii will flower in December, thus the common name Christmas cactus.
A related species, Schlumbergera truncata, from the same region blooms a month earlier and is commonly known as Thanksgiving cactus. Both plants grow vegetatively by producing flat, leaf-like stem segments connected at the mid-veins. The two species are similar except Schlumbergera truncata has 2-4 saw-toothed serrates along the leaf/stem margins, cylindrical ovaries, and yellow anthers while Schlumbergera bridgesii has dentate margins, 4-5 angled ovaries, and purple anthers.
Considerable breeding has resulted in a wide selection of flower colors, branching density, uprightness, flattened stem shape, flower shape, and bloom time. Although flower color is the primary criterion which consumers evaluate, producers are more likely to be concerned with the ability of specific cultivars to bloom in time for holiday sales. Many cultivars available are the result of crosses between Thanksgiving cactus and Christmas cactus.
Nighttime temperature and photoperiod influence flowering. Christmas cacti will develop buds and bloom if given bright light, short days, and night temperatures between 55 and 65F. Plants initiate flowers under short-days (8-10hours) at 60 to 68 (15.5-20C) and remain vegetative under long-days. Flowering is delayed by night temperatures greater than of 68F (20C) under short-days. Plants require at least 20-25 days of continuous short-days (7 days a week) to initiate flowers and buds are visible to the naked eye in 3-4 weeks. However, it is important to provide 6 weeks of short-days for complete bud set. Photoperiod has no effect on flower development once initiation has occurred. However, temperature can be raised or lowered to manipulate the speed of flower development once buds are visible. Total flowering time is 7-8 weeks at a 68F night temperature and 9-10 weeks at 60F. Two hours of night interrupted lighting (11:00 pm - 1:00 am) will inhibit flowering under photoinductive conditions. Night interrupted lighting is required from October 1 to March 1 to keep plants vegetative. Black cloth can be applied from 5:00 PM to 8:00 AM to induce flowers under noninductive photoperiods. Plants can be covered with black cloth from March 15 to September 15 to insure flower bud formation. Full sunlight is beneficial during fall and winter, but excessively bright light during summer months can make plants look pale and yellow.
Christmas cacti require less water from October to March than they do when actively growing from April to September. A rest period is very important if plants are to bloom abundantly. Dormancy should be started about the middle of September and continued for 8 weeks. Care should be taken that the soil never becomes waterlogged during the short days of winter. Water early in the day so the foliage will dry quickly, thus helping to prevent the likelihood of disease.
Since these cacti are epiphytic plants that, in their native environment, root into decaying organic debris trapped among tree branches or in rocky crevices on the ground, they like an exceptionally course, well-drained medium with high porosity. Many growers use pure, course peat moss, though various ratios of peat (80-60%) and perlite (20-40%) work well. Coarse builders sand and styrofoam beads have also been used as media components. The growing media should have a pH of 5.5-6.2.
For more information about landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.
Virginia Cooperative Extension will be offering Master Gardener classes in Albemarle, Fluvanna, Louisa, and Nelson counties beginning in January. Please call your local Extension office for more information.