The exotic, tropical blossoms spill over the sides of the flowerpot at Christmas, brightening the room despite the gloomy winter weather. A traditional holiday plant, the Christmas cactus (Schlumbergera bridgesii) blooms in December when it receives 12 to 14 hours of darkness, cool night temperatures and sufficient humidity. The rest of the year, a Christmas cactus is a relatively easy-care houseplant.
Keep It Comfortable
While called a cactus, this tropical epiphyte is native to Brazil, where it lives in the branches of trees, much like an orchid. It enjoys a summer vacation in a warm, shady garden outside, but is hardy only in U.S. Department of Agriculture plant hardiness zones 11 and up. When night temperatures dip toward the 50s, it is ready to go back inside to a cool room with bright, filtered light.
While Christmas cactus is primarily grown as an indoor plant, USDA zone 10 gardeners who have a well-drained, warm, shady corner with a microclimate that never drops below 50 degrees Fahrenheit might grow Christmas cactus outdoors. Plant the cactuses in hanging pots or in the ground, spaced 24 inches apart. Monitor weather reports carefully for cold weather and frost warning, and bring potted plants indoors or protect the in-ground cactuses by covering them with plastic sheeting.
During its growing season, from April to September, the Christmas cactus prefers temperatures between 70 and 80 degrees Fahrenheit. As the days shorten and the weather cools, it begins setting buds for its spectacular winter blooming.
Quench Its Thirst
Unlike desert cactuses, the Christmas cactus' soil should never dry out completely. When the soil is dry to the depth of 1 inch, put the flowerpot in the sink and add water until it flows from the bottom of the pot. Wait a few minutes, then repeat the watering to ensure that the planting medium is thoroughly moistened. After the water has drained from the flowerpot, return the Christmas cactus to its usual place. If the flowerpot is too large or heavy to move, use an old turkey baster to remove the water from the pot's saucer. Do not leave the bottom of the pot standing in water; Christmas cactus, like orchids, do not like wet feet.
Water outdoor Christmas cactuses when the soil is dry to a depth of 1 inch. Monitor outdoor plants carefully in hot weather to ensure that the soil doesn't completely dry out around their tender roots.
In addition to regular watering, the Christmas cactus prefers a higher humidity than most homes can provide. Grouping plants together on a tray filled with pebbles and water and adding a cool steam humidifier helps raise the moisture in the air. Avoid placing a Christmas cactus near a heating or air conditioning vent; the air is too dry.
Feed It Regularly
When new growth appears in early spring, the Christmas cactus needs regular feeding. Feed the plant with a 20-10-20 or 20-20-20 liquid fertilizer, mixing 1 teaspoon of fertilizer with 1 gallon of water. Fertilize monthly, immediately after watering. Pour the fertilizer over the soil until it drains from the bottom of the flowerpot.
In addition to fertilizer, Christmas cactus need magnesium. Mix 1 teaspoon of Epson salts with 1 gallon of water. Add the solution to the plant's soil immediately after watering, two weeks after fertilizing. Do not use fertilizer and magnesium in the same week.
Feed outdoor cactuses in the same way, adding fertilizer and magnesium on the same schedule as indoor plants. Always fertilize after watering to ensure that the fertilizer salts don't burn the plants' tender roots.
Stop feeding the plant after September.
Make It Bloom Again
A Christmas cactus prefers to be pot bound. Repot in spring using a light, well-draining potting mix, such as an African violet or cactus mix with high organic matter, in a slightly larger clay or plastic flowerpot. Like orchids and other epiphytes, a Christmas cactus prefers a neutral to slightly acidic soil pH, between 6.0 and 7.2.
When September arrives:
Reduce temperatures in the room to 50 to 59 degrees Fahrenheit at night and 65 to 68 degrees during the day.
In mid-September, cover the plant from approximately 6 p.m. to 7 a.m. every day.
Also in mid-September, remove new leaf segments that are less than 1/2 inch in length.
Water sparingly, keeping the soil slightly moist.
Keep the humidity high to prevent bud drop.
Christmas cactus develop flower buds when they receive 12 to 14 hours of uninterrupted darkness for six weeks. After the flower buds have formed, you can stop covering the plant.