Answer: Successfully growing Christmas cactus starts with a potting mix that is well drained and has good aeration. To make your own, mix one part potting soil, two parts peat moss or compost, and one part sharp sand or perlite. Christmas cactus do not mind being potbound and will need repotting only once every three years. Full sunlight is beneficial in midwinter, but during the summer months, filtered light is preferred. Bright sun during the summer months can make plants look pale and yellow. During the growing season, from April to September, optimum growth occurs when daytime temperatures are kept between 70 to 80F. Like other houseplants, they prefer night temperatures 10 to 15 degrees cooler. Water when the growing medium is dry to the touch. The Christmas cactus is tolerant of dry, slightly under-watered soils. Avoid excessively dry soil, however, as well as waterlogged soil. Water requirements will be reduced from fall through spring which means watering should be less frequent.
Fertilizing is not necessary during the fall and early winter. Begin fertilizing as new growth begins in late winter or early spring. Use a soluble fertilizer at one quarter of the recommended rate and fertilize monthly. Good flower bud production requires controlling temperature and the amount and intensity of light received by the plant. Exposing a Christmas cactus to 50 F. continuously during September and October, without manipulating lighting, will stimulate bud production but this would be difficult for most homeowners. To ensure good flowering, provide bright light during the day, cool temperatures at night (55 to 65F.) and periods of continuous darkness. For eight weeks, beginning in mid September, provide 13 hours of uninterrupted darkness each night. The plant can be moved to a closet or a paper bag can be placed over it to achieve this effect. The dropping of unopened buds is a common problem when growing Christmas cactus. This can be the result of excessive bud set but is sometimes related to environmental conditions. Sudden changes in temperature or light, as well as very dry soils, can cause buds to drop. Continuous warm temperatures (above 90F.) will have the same effect.
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