Christmas cactus (Schlumbergera bridgesii) produces red, pink, lavender or peach blooms during the winter months when the temperatures are right for healthy growth. This tropical cactus can only grow oudtoors in U.S. Department of Agriculture plant hardiness zones 11 and 12, so it's most often grown as a houseplant. Although it can't tolerate cold, it performs best in the winter in cooler temperatures.
Spring and Summer Temperatures
Christmas cactus requires moderately warm temperatures during its active growing season, which lasts from spring, after flowering is complete, until late summer when the plant begins to prepare for the next flowering season. Maintain temperatures between 70 and 80 degrees Fahrenheit. Although you can place the plant outside during the summer, avoid setting it out if temperatures are below 50 F. Place the cactus in an area with bright but indirect sunlight, because direct light can scorch the plant.
Although the Christmas cactus responds better to lower temperatures in fall when it's beginning to set flower buds, it still cannot tolerate temperatures lower than 50 F. Buds won't form if the temperature is too high or if the plant receives too much light. Maintaining temperatures between 60 and 68 F while providing 14 hours of complete darkness every night for six weeks, beginning in mid-September, help ensure the maximum amount of flowers during the winter blooming season. Maintain the lower temperatures through winter to help the flowers persist as long as possible.
If absolute darkness each evening isn't possible, you can use lower temperatures to force bud formation. Provide the cactus with as much darkness as possible, but keep it in a continuously cool spot. The cactus will form flower buds if temperatures remain between 50 and 59 F, but avoid lower temperatures as these may damage or kill the cactus. The cactus may not form as many buds with this method as with controlled hours of darkness.
Temperatures above 90 F can harm Christmas cactus, especially when flower buds are forming. The buds drop off in high temperatures, so avoid placing the cactus in overly warm, sunny spots or near heat vents. Temperatures below 50 F also cause bud drop and slow down the cactus growth. Prolonged periods of less than 50 F may eventually damage or kill the plant. Freezing temperatures will usually kill a Christmas cactus.