The Christmas cactus (Schlumbergera truncata), also called the crab cactus, is a blooming houseplant that's native to Central and South America. Although it is part of the cactus family, the Christmas cactus has care requirements more like a tropical plant than a desert cactus. Blooming with showy, white and bright-pink flowers, the Christmas cactus' name comes from the fact that its blooming period is during late fall and early winter. The Christmas cactus is easy to care for, but some special attention to the plant is necessary to encourage it to bloom.
Place your Christmas cactus in a cool location where it will be in bright, indirect sunlight during the day and total darkness at night. Keep the cactus away from direct sun; instead, place the plant near an eastern-exposure window.
Water your Christmas cactus moderately and evenly once per week during spring and summer, or when the top 2.5 cm (1 inch) of potting soil is completely dried out. Provide just enough water to moisten the potting soil, but not drench it.
Keep humidity levels at about 50 to 60 per cent around your Christmas cactus by placing the pot on top of a drainage dish filled with gravel and water. Ensure that the pot is sitting on top of the gravel and not in the water.
Feed your Christmas cactus a liquid 0-10-10 NPK (nitrogen, phosphorus and potassium) fertiliser in late October or early November and again in February. From April through September, feed the Christmas cactus once a month with a liquid all-purpose houseplant fertiliser, according to the directions on the label.
Prune your Christmas cactus in March or early April. Pinch back the old growth to encourage new blooms.
Provide a resting period for your Christmas cactus for about 30 days in January. Place the Christmas cactus in a cool room and cut back on watering to only one or two light waterings during the resting period.
Encourage blooming during the holiday season by watering your Christmas cactus only once per month during autumn and early winter. Keep the plant in a spot where air temperatures are around 10 degrees Celsius (50 degrees Fahrenheit), but never below freezing.
You can repot your Christmas cactus during February through April, but the plant flowers best when it's kept pot-bound. Repot the Christmas cactus only once every two years or so.
Never place your Christmas cactus in a draughty location or near heating and cooling vents; avoid dramatic fluctuations in air temperature and humidity.