The exotically beautiful red -- or pink, white or purple -- flowers of the Christmas cactus (Schlumbergera bridgesii), highlighted by its waxy succulent-like green leaves, bloom during the winter holidays indoors, if correctly prepared, or naturally in the tropics where it grows in the nooks and crannies of trees. As the kids eagerly watch for budding that tells them Santa's just around the corner and moms scramble to get everything done, the Christmas cactus may be under some stress too. If the leaves turn red, the plant is ill from too much or too little sunshine, water, heat or cold.
Excessive light is the likeliest cause of red leaves. The leaves may even suffer sunburn if the succulent is in direct sunlight too long. Although a Christmas cactus can spend warm months outside if the location isn't too dry, this plant, native to the rain forests of Brazil, needs shade or filtered sunlight. Inside, the plant fares best in bright but indirect light. Set it within 6 feet of a window facing south, east or west. As Christmas approaches, the cactus needs at least twelve hours of darkness daily to prepare for the flowering process.
Rain Forest Moisture
The Christmas cactus requires more water than most cacti or succulents. Limpness sometimes accompanies red leaves if the blame can be laid on too dry growing conditions. When under drought stress, the rain forest plant wilts. Water thoroughly whenever the top inch of soil feels dry to the touch. Christmas cactus must grow in well-drained soil. Pot it in a commercial mix especially for cactus, or mix your own by combining two parts standard potting soil with one part vermiculite or clean sand. If your home, like many, is dry in winter, fill a shallow saucer with pebbles and add water. Set the potted Christmas cactus on top of the pebbles -- the water should not reach the bottom of the pot, which could lead to overwatering instead of simply raising humidity.
Another stressor that may contribute to a Christmas cactus's leaves turning red is a temperature uncomfortable to the plant. If the cactus sits next to a frosty window, it can suffer from too much cold. On the other hand, it does not have the heat tolerance of many cactuses. Keep your plant away from drafts, as well as heat sources, such as vents, fireplaces or televisions. These tropical beauties enjoy temperatures between 70 and 80 degrees Fahrenheit during the day, dropping to 55 to 65 degrees Fahrenheit at night.
Most Christmas cactus owners want their plants to bloom as extravagantly in the years to come as they did when first purchased. Sometimes a Thanksgiving cactus (Schlumbergera truncata), which blooms in late November, is mistaken for a Christmas cactus. A true Christmas cactus has scalloped stem segments and produces blooms at the stem tips. To encourage rebloom, begin placing your plant in a dark closet each day from 8 p.m. to 8 a.m., beginning about mid-October.
If you can, leave your cactus outside in temperatures above freezing but below 55 degrees Fahrenheit, however, the plant will set flower buds regardless of the length of the day or night. The Christmas cactus, a tropical rain forest plant, is cold-hardy in U.S. Department of Agriculture plant hardiness zones 9 and 10.