by Bruce Brethauer
The Christmas Cactus is perhaps one of the most familiar and commonly grown of the cactus species. It is widely available through the holiday season, being a standard at virtually any garden department. These are easy plants to grow and maintain, tolerating a wide variety of growing conditions and benign neglect. Where they are happy, they prove to be very long lived plants; (at one of our shows, a patron indicated that a member of his family was growing a Christmas cactus which had been passed down from his grandmother, and estimated that this plant had been in the family for over 90 years! Another plant in the possession of one of our members is estimated to have been passed down through the family for 150 years)! With a little bit of attention to basic requirements, these have also proven to be easy to bloom - reliably flowering every year (and some growers report that their plants frequently produce flowers 2 and even 3 times each year).
The Christmas cacti belong to the Genus Schlumbergera (or in some classifications Zygocactus), and are native to the costal mountains of south-eastern Brazil at higher elevations (to about 6000 feet). Six species are recognized, but 2 or 3 species and their hybrids account for the majority of plants in cultivation. Those plants which are most frequently seen at Ohio nurseries are derived from S. truncata, followed by plants derived from S. russelliana. In habitat, the Schlumbergeras typically grow epiphytically, growing on the trunks and branches of the forest trees, or lythophytically (growing on rocks); they frequently grow in association with mosses, ferns, orchids, and bromeliads. These plants grow in conditions that are typically cool, moist, and somewhat shaded.
The stems are highly modified, with flattened segments that have a very leaf-like appearance. The margins of the stems are either coarsely toothed, (in the Truncata group) or with rounded teeth (in the Buckleyi Group). Stems typically grow in long branching chains which initially grow more or less upright, but as these branches grow larger, become more arching and pendant. In time, the plants can achieve surprisingly large sizes – I have seen plants approaching 4 feet in diameter, and I suspect that they can grow larger still. But these plants can easily be maintained at considerably smaller sizes by pruning away any unwanted growth.
Flowers are long and tubular, with curving to reflexed petals which gives the flowers a bilateral symmetry (there is only a single line which can divide the flower into two mirror images); in contrast, the majority of cactus flowers have a radial symmetry in which any line drawn through the center of the flower will produce a mirror image (sunflowers have radial symmetry- orchids and pansies have bilateral symmetry). In this photo showing the underside of the flower, this trait shows especially well. The tubular shape and the bright coloration of the flowers are adaptations to attract hummingbirds, which are believed to be the primary pollinators of these flowers in habitat. While the range of flower colors in the wild species is highly variable, Christmas cacti have been selected and hybridized to produce an extended range of flower colors and color combinations (many cultivars have bi-and tri-colored flowers). While magentas and reds predominate, many cultivars produce a huge range of colors through pink, white, or yellow.
Flower buds are primarily produced on new growth, so it is a good idea to give the plant a good spring pruning to encourage more branching, to keep the plant more compact, and to promote greater production of flower buds. While some sources suggest that lower temperatures in the fall will help to stimulate the production of flower buds, it has been my observation that this is not necessary, and that most plants will produce flowers in response to changes in daylength; plants respond to the shorter daylight hours of autumn by producing flower buds. Plants which are grow exclusively in the interiors of homes where they see little daylight will seldom produce flowers; while plants which are grown where they receive their light predominately from natural sources will readily flower in the late fall and early winter (at least in the northern hemisphere - in habitat, these plants typically flower in the month of May).
The Christmas cacti are easy to grow, but they are adapted to somewhat different growing conditions and should be treated differently than succulents from more arid regions. These plants are adapted to conditions which are comparatively moist, cool, and shaded; they prefer conditions of bright, but diffuse light, and may not be at their best when grown in direct full sunshine. Sunny windows are good, but if you are in the habit moving your plants outdoors to the patio during the spring and summer, it is best to grow these plants in dapple shade. If you grow this plant in a hanging basket, these can be hung from the lower branches of shade trees during the warmer months.
Even though these plants can and will survive through periods of drought, for best growth, they should not be subjected to extended drought. During the warmer months from spring through early fall, it would probably be best to keep these plants evenly moist to barely moist. If the plants are showing signs of producing flower buds in the fall, or are in full bloom, they should not be permitted to go completely dry, otherwise the flower buds and flowers may be dropped to conserve water. During the winter (after the plant has finished flowering) it would probably be best to keep it somewhat drier, allowing it to remain dry for a while between waterings. The soil for these plants still needs to be porous and well draining, but should retain water longer than soils marketed for other cacti and other succulents. Various growers have used many different growing mediums; I have seen plants grown in everything from standard potting mixes for foliage plants to ordinary garden dirt, and they seem to do ok in just about anything, so the soil is not necessarily critical- but I believe that they will do best in something which is well draining but with a higher degree of organic material (peat moss and coir for example) I suspect that a mix for phalenopsis orchids would work best. This is a fast growing plant, so it will benefit from more frequent fertilization than other cacti - I still recommend a dilute mixture of a water soluble fertilizer such as Peters or Miracle Grow -but at 3 week intervals through the growing season. Despite the fact that these plants originate from comparatively cool habitats in the wild, they seem to thrive at pretty warm temperatures (mid 80's to low 90's), easily tolerating our summer temperatures so long as they are kept out of the direct sun and kept reasonably moist. Growers in hotter regions (Arizona and Nevada for example) may have difficulty maintaining these plants outdoors in the summer months - no matter how much shade and moisture they provide. These plants are more cold tolerant than most people would imagine - many wild populations experience night temperatures to below 40 degrees, and some populations are said to experience temperatures to below freezing in habitat. Curiously, exposing these plants to cooler temperatures (below 57 degrees Fahrenheit) while they develop their buds and flowers can intensify and modify their flower colors. While I do not recommend subjecting these plants to freezing temperatures, they probably should be given a cool and comparatively dry dormancy period following their blooming season.
Christmas cacti are deservedly popular plants - easy to grow, tolerating a wide range of growing situations, and tolerant of reduced light levels, making them better suited as houseplants than most other succulents. Best of all, they put out a fantastic display of vibrantly colored flowers in the late fall and early winter when few other plants are flowering. Their comparatively small size, makes them well suited to compact spaces, and the stems of the two most commonly grown species are spineless, and non toxic, making these plants suitable for households with inquisitive pets and very young children. The attractive arching branches of these plants show especially well in hanging baskets which can easily be hung from the lower branches of shade trees from spring through early fall. These plants are resistant to most insect pests, and are tolerant of neglect and drought - they will not whither and die on you if you forget to water them for a week or two - neither will they quickly turn to mush if they are occasionally overwatered. Through their growing season, they will not drop leaves on the ground (although following their flowering period, you will need to sweep up their fallen flowers). They are also widely available at reasonable prices (albeit only seasonally) from practically any nursery department. If you have never grow a cactus before - these make a great plant for novices, and children. If you are a long time grower of succulents, but haven't grown this plant in years, you might consider giving these plants another look this year.