Eddie Seagle is a Sustainability Associate, Golf Environment Organization (Scotland), Agronomist and Horticulturalist, CSI: Seagle (Consulting Services International), Professor Emeritus and Honorary Alumnus, Abraham Baldwin Agricultural College, and Associate Editor of The Golf Course, International Journal of Golf Science. Direct inquiries to eddie@csiseagle.com.

Popular house plants which gain notoriety at this time of the year are the Thanksgiving cactus, Christmas cactus, crab cactus and holiday cactus. These are all Schlumbergera cultivars and are available in white, pink, yellow, orange, red or purple flowers. The Easter cactus or Whitsun cactus (aka a holiday cactus) has intense scarlet flowers and is in a different genus (Hatiora).

The Schlumbergera cultivars are classified into two main groups, the Truncata Group and the Buckleyi Group.  The Truncata Group consists of all the cultivars with characteristics of the Schlumbergera truncate including stem segments with pointed teeth, flowers positioned horizontally, and yellow pollen. These cultivars include the Thanksgiving cactus, crab cactus and claw cactus, and they generally flower earlier in the season than the members of the Buckleyi Group.

The Buckleyi Group contains those cultivars with characteristics of the Schlumbergera russelliana including stem segments with rounded, more symmetical teeth, regular (symmetrical) flowers which droop down below the horizontal, and pink pollen. These cultivars include the Christmas cactus and generally flower later in the season than members of the Truncata Group.

Hundreds of modern selections from Europe, North America and Australia have been placed into several cultivar groups. Other such groups include the Reginae Group containing those cultivars with characteristics from hybrids with Schlumbergera orssichiana and the Exotica Group that is applied to the small number of hybrids associated with Schlumbergera opuntioides.

The Thanksgiving cactus (Schlumbergera truncata) and the Christmas cactus (Schlumbergera bridgesii) are both very popular flowering houseplants for the fall and winter seasons. They are native to Brazil and are available in red, rose, purple, lavender, peach, orange, cream, and white colors. These Schlumbergera species can be found growing as epiphytes among tree branches in their native shady rain forests. Also, their characteristically pendulous stems make them a great selection for use as hanging baskets.

When grown in an environment offering proper night lengths and conditions, the Thanksgiving cactus usually flowers around Thanksgiving day and about a month before the Christmas cactus begins to bloom.  The length of flowering can last up 8 weeks under proper conditions at about 68 ºF. The other holiday cactus, the Easter cactus (Rhipsalidopsis gaertneri), flowers in the spring and occasionally throughout the year and exhibit either pink or red flowers.

The flattened stem segments help distinguish between the Thanksgiving cactus and the Christmas cactus. The stem segments on the Thanksgiving cactus have 2 to 4 saw-toothed serrations along the margins while the stem margins on the Christmas cactus are more rounded. Since there are no true leaves on either of these holiday plants, the photosynthetic process occurs within the green stem segments.  Another identifying characteristic between the two cacti involves the color of the pollen bearing anthers (yellow in the Thanksgiving cactus and pink to purplish-brown in the Christmas cactus).

Generally, these holiday cacti grow best in light shade. However, full sunlight is beneficial during fall and winter seasons, but full sun during the summer months can cause the plants to appear pale and yellow. The optimum spring and summer growth occurs at temperatures between 70 to 80 °F during the growing season from April to September.

However, the Thanksgiving and Christmas cacti depend upon shorter day lengths (8 to 10 hours) and cooler temperatures to set their flower buds in the fall. Do not allow the microenvironmental temperatures to reach 90 °F once the flower buds are set in the fall. Such continuous warm temperatures can cause flower buds to drop. Furthermore, do not leave these cacti outside if the outside temperatures drop below 50 ºF. The secret of quality flower bud production during the fall involves effective temperature regulation and photoperiod (length of day and night) management.

To initiate flower buds the cacti need intense light and long nights. About 14 hours or more of continuous darkness each day is required for flower bud set beginning the middle of September and continued for at least 6 weeks for complete bud set. Any interruption in this dark period will prevent flower bud set. The flower buds will be visible in 3 to 4 weeks and the photoperiod does not have any effect on flowering once the buds are set.

Also, the fall growing temperatures should be kept between 60 and 68 °F with maximum flower production at about 68 °F. Those plants grown with night temperatures between 50 and 59 ºF will set flower buds regardless of day length, but growth will be slower and bud drop may occur if the temperature remains at or about 50 ºF.

Maintain sufficient moisture levels to prevent excessive wetting or drying of the soil media. Fertilize the cacti monthly from new growth in late winter or early spring and throughout the summer using a one-half dosage of soluble fertilizer (20-10-20 or 20-20-20 with trace elements). Holiday cacti have a higher requirement for magnesium than many plants. Therefore, fertilize monthly during the growing season with Epsom salts (magnesium sulfate) mixed at 1 teaspoon per gallon of water, but do not apply the same week as the regular fertilizer. Stop the fertilization program during the late summer for greater flower bud production in the fall, but continue to water as needed.

These holiday cacti are easily propagated by cuttings which can be taken in May or June. Pinch off sections of stems with 3 to 5 stem segments on each and allow the cut ends of the sections to callus by placing them outdoors in the shade for a day or two. Use a well-drained potting soil medium and place three cuttings at approximately one inch deep into the potting soil of a 4-inch container or use 5 cuttings in a 6-inch container. Sufficiently water the soil and cover the plants and rooting container with a clear plastic bag secured with a rubber band or other wrap around the container. The plastic bag will serve as a miniature greenhouse and maintain the relative humidity at peak to promote rooting. Place the container in bright, indirect light until roots have formed in three to eight weeks. At this time the plastic bag can be removed, and a diluted fertilizer solution can be applied to feed the cacti.

The major disease problem of the holiday cacti is root rots which can often be prevented by avoiding excessive watering. Also, insects and related pests include aphids, fungus gnats, mealybugs, red spider mites, and soft brown scale. Keep a close eye on any such activity and respond accordingly.

May you achieve total satisfaction and ornamental appeal from your dedicated and sustainable gardening efforts during this Christmas season as your Christmas cacti come into full bloom providing awesome color. Merry CHRISTmas to all!