Light
Unlike other Cactaceae, epiphytic cacti should not be placed in direct sunlight in summer. Bright, filtered light is ideal in spring and summer, while a few hours of full sun will help them thrive in fall and winter.
Soil
The soil should be porous to ensure good drainage and aeration. They like a slightly acid mix (pH of 5.0 to 6.0). You may wish to make your own mix of 40% perlite and 60 % sphagnum moss, or 5 parts potting soil and one part perlite or coarse bark.
Temperature
They normally like the ambient room temperature in our homes. It is good to put them outside in a shady spot in summer and bring them back in before the first frost. The ideal daytime temperature is about 20°C, and about 5° lower at night. The temperature should never drop below 10°C in winter.
Humidity
In spring and summer, it is best to soak these plants from time to time. In fall and winter, avoid placing them close to heat sources so they won’t dry out. They like to be misted in dry weather.
Watering
In their natural habitat, rainfall varies from 37 cm a month in winter (December to March) to 3 cm a month in summer. This means that epiphytic cacti always require humidity. The soil should be allowed to dry out slightly, but never completely, between waterings. These cacti can be killed by over- or under-watering.
Feeding
A balanced water-soluble fertilizer, such as 20-20-20, may be applied once a week, at one-quarter the recommended dosage, during the growing season. Stop feeding the plant about three months before it blooms, i.e. in September for a Christmas cactus. During this rest period, cut back on watering and lower the temperature to encourage the plant to set new flower buds, which form on that year’s segments. Start feeding again after it has finished blooming.
Propagation
These cacti may be propagated from seed, although taking stem cuttings is a faster method. Stem cuttings may be made at any time, but be careful to keep the soil temperature at 20°C in winter. First remove from 1 to 4 segments from the ends of a few stems. Let them dry out for a few hours to allow a callous to form and prevent the cuttings from rotting. Then simply place them in soilless potting mix or a mixture of equal parts peat moss, sand and perlite.
It will normally take from 2 to 3 weeks for roots to appear. Transplant the cuttings into potting soil and cut them back to 2 segments in May or June to encourage the stems to branch out and set buds.
Blooming
New floral buds develop on previous year's growths. Pruning these would delay blooming for a full year.
You can encourage a Christmas cactus to form flower buds by adjusting the temperature or the amount of daylight (photoperiod) it receives, or both.
Controlling the temperature
Keep the nighttime temperature at about 15°C. Higher temperatures will encourage more vegetative growth rather than buds, while lower temperatures may delay blooming by 2 to 4 weeks.
Controlling the amount of light
Provide 14 to 16 hours of total, uninterrupted darkness every day for 6 weeks. The plant requires normal light conditions during the daytime, however. At home, you can simply place a large cardboard box over the cactus at about 5 p.m. and remove it the next morning at about 8 a.m.
Ideal conditions, then, are 6 weeks of short days: 8 to 10 hours of daylight daily, at 20-21°C, and cooler at night, about 15°C. Continue watering as usual. No matter which method you use, return the plant to its normal conditions as soon as the buds have set.
Important
These methods should be used only for Christmas cacti. Epiphyllums and Hatioras do not require this kind of treatment. For them, blooming is initiated by cooler wintertime temperatures and a shorter photoperiod, coupled with less frequent watering.
Pests, diseases and physiological disorders
Wilted leaves indicate that a plant has been over- or under-watered. Poke a finger into the soil to check how moist it is, and avoid leaving any excess water in the saucer.
In general, these plants cope better with too little rather than too much water. This means that they should be planted in well-drained soil. Poorly drained soil or over-watering will usually encourage the growth of pathogens, leading to root rot. These cacti may also be attacked by mealybugs. Remove them with a cotton swab dipped in rubbing alcohol and rinse well afterward to avoid burning the plant.
Another common problem is bud drop, caused by too much heat, too little water or moving a plant in bloom. To avoid this problem, keep the plant at about 19°C and try not to move it while it is in bloom.