Culture
The Thanksgiving cactus is also commonly called the holiday or crab cactus. It grows best in light shade. Full sunlight is beneficial in midwinter, but bright sun during the summer months can make plants look pale and yellow. Ideal growth occurs at temperatures between 70° and 80° F during its growing season from April to September. Do not let temperatures rise above 90° F once the flower buds are set in the fall. Continuous warm temperatures can cause flower buds to drop.
The secret of good flower bud production involves temperature and dark (photoperiod) control. For best flowering provide 1) Bright light, 2) Night temperatures between 55° and 65° F, and 3) Long nights – thirteen hours or more of continuous darkness each day is required before flowering will occur. Long nights should be started about the middle of September and continued for eight weeks.
Water the growing medium when it is dry to the touch. The holiday cactus is tolerant of dry, slightly under-watered conditions. Do not let the soil become waterlogged, especially during the dark days of winter. Do not let the soil dry out either. Reduce watering from fall through spring. Fertilize plants monthly from the time new growth starts in late winter or early spring, and throughout the summer using a one-quarter strength soluble fertilizer. Reduce fertilizer during the fall and early winter.
The Thanksgiving cactus flowers best when kept somewhat potbound. Repotting is necessary only about once in three years. The potting media must be well-drained with good aeration, because the plant does not grow well in heavy, wet mixes. A good mix may contain one part potting soil, two parts peat moss and one part sharp sand or perlite.
Noteworthy Characteristics
Schlumbergera truncata, commonly called crab cactus, Thanksgiving cactus or holiday cactus, is all the same plant. It is a popular, winter-flowering houseplant native to Brazil, available in a wide variety of colors including red, purple, oranges, pinks and creams. In its native environment, these cacti grow on rocks or in trees where hummingbirds pollinate the flowers. The stems are segmented, flattened to round in cross-section, with weak or no spines. The stems are graceful and arching and are an easy-care plant for most homes.
Genus name honors Frederick Schlumberger, Belgian horticulturist.
Specific epithet mean cut off square.
Problems
This cactus commonly drops unopened flower buds, which may be induced by an excessive number of buds or a sudden change in temperature, light or other environmental factors, such as drying out of the growing medium. Lack of flowering is often due to light interrupting the long night period (13 hours) that is required for flowering initiation to occur. The major disease is root rot, which can be prevented by avoiding excessive watering. Insects and related pests include mealybugs, soft brown scale, red spider mites and aphids.
Uses
In its native area, Schlumbergera truncata is grown outdoors as an epiphyte or in rock gardens. In cooler climates, this plant can be grown in baskets or pots for brightly-lit window sills. It is sold primarily around the holiday season as a gift or decorative item.