Christmas cactus plants (Schlumbergera bridgesii) are epiphytes that grow naturally in trees in Brazil. They absorb moisture and nutrients from debris that gets caught in the tree branches. Commonly grown as houseplants, they can also be grown outdoors in pots in U.S. Department of Agriculture plant hardiness zones 9 to 11, as long as they are brought indoors if the weather gets too cold. They can survive temperatures down to 20 degrees Fahrenheit, but their stems will be severely damaged.
Light and Temperature
Place indoor Christmas cactus plants in bright, indirect light. Right next to a south-, west- or east-facing window is ideal. Direct sunlight will cause these plants to turn yellow or develop a reddish blush and the stems may droop. The flowers will be a lighter color in direct sunlight, and they will fade and die more quickly.
Outdoor Christmas cactus plants can be grown where they get direct sunlight only in the morning, dappled shade all day or in bright shade. Ideally, bring them indoors when temperatures drop below 50 degrees Fahrenheit.
Give Christmas cactus plants 14 hours of complete darkness every night and maintain temperatures between 60 and 68 degrees Fahrenheit beginning around mid-September for a good show of flowers around Christmas. Flower buds should be set after four weeks. After the flower buds form, there is no need to provide complete darkness at night, but do not allow the temperature to rise above 90 degrees Fahrenheit. If it gets too hot, Christmas cactus plants drop their flowers.
Water Christmas cactus plants when the top 1 inch of the potting mix feels dry. Pour room-temperature water evenly over the potting mix until it drains from the bottom of the container. Cold, fresh tap water could chill the roots. Avoid splashing water on the stems as this could lead to fungal disease.
After the Christmas cactus forms flower buds, water it when the top of the mix just begins to dry. The top of the potting mix should not become completely dry before watering. If the potting mix dries out during bloom, the cactus may drop its flowers.
Christmas cactus should never be planted in the ground or in garden soil. Water will not drain away from the roots quickly enough and they will develop root rot.
Give Christmas cactus plants fertilizer every four weeks from late winter when it begins to put on new growth to late summer. Water-soluble fertilizer with a ratio of 20-20-20 or 20-10-20 that contains trace elements is ideal for these cactuses. Mix the fertilizer into water at only half the recommended rate. A common recommended dilution rate is 1 teaspoon of fertilizer per quart of water, but this varies, depending on the fertilizer formula. Therefore, for Christmas cactus, use only ½ teaspoon per quart of water.
Also, give the Christmas cactus 1 teaspoon of Epsom salts dissolved in 1 gallon of water every four weeks but not at the same time as the fertilizer. Give them the Epsom salts one to two weeks after the fertilizer.
Do not provide fertilizer or Epsom salts after late summer. It will inhibit flowering.
Pinch off one segment from each stem in late spring to encourage the Christmas cactus to grow more branches which will result in more flowers. Wash your hands before pinching. There could be bacteria on your hands that could cause stem rot.
At the beginning of September, pinch off any segments at the ends of the stems that are less than ½ inch long. They are not mature enough to produce flowers. The longer segments left behind will produce flowers.
Root rot is the most prevalent disease in Christmas cactuses. Proper watering and potting mix can prevent this disease. The first symptom of root rot is wilting. As the roots die, they are unable to supply the Christmas cactus with moisture and nutrients. The stems may also turn yellow or develop red edges as the disease progresses. If the cactus has just begun to wilt, it may be possible to save it. Remove the cactus from its pot and examine the roots. If more than half the roots are dark and mushy or wiry, the plant should be thrown away. When most of the roots are still white, firm and healthy, it could be saved. Cut the rotten, dark mushy or wiry roots off at the base with disinfected scissors. Disinfect the scissors with household disinfectant, rinse and dry them. Repot the cactus in a new clay pot with a drainage hole with fresh potting soil and do not water it for one week after repotting.
Mealybugs and scale insects are the most prevalent pests of Christmas cactus. They are slow-moving or immobile insects that pierce the stem sections and suck plant juices out. Mealybugs are small, flat, oval bugs that are white and mealy looking. Scale insects are flat and usually tan, but they can be other colors.
As soon as they are detected, use a cotton swab soaked in rubbing alcohol to wipe them off or scrape them off with your thumbnail or an old toothbrush.
Check Christmas cactus plants carefully for these pests before bringing them in if they have been outdoors.