Kids may not carol about cactuses, but the bright red, white or pink blooms of Christmas cactus (Schlumbergera bridgesii) are just as festive as other holiday plants, and don't look out of place the rest of the year. Christmas cactuses bloom on the tips of trailing stems up to 3 feet long, made up of flat, succulent segments, called phylloclades. While they require a period of uninterrupted dark to bloom again in December, you can move a Christmas cactus outdoors for the summer if conditions aren't too hot, and keep it outside year-round in the frost-free climates of U.S. Department of Agriculture plant hardiness zones 10 through 12.
1. Preparing for the Move
Pinching back the stems in late spring as new growth begins, by snapping stems at the joints between the phylloclades, promotes branching and more flowering tips. Generally clean the plant up, removing any dead stems, and now would be the time to repot if your plant needs it. Christmas cactuses tend to bloom more when they're potbound though, and should only need repotting every three years or when the root mass is straining against the sides of the pot. Move the plant to a brighter, cooler area inside your home for a week or two to begin the transition outdoors.
When nighttime temperatures are reliably above 50 degrees Fahrenheit and from 70 to 80 F during the day, you can start bringing your Christmas cactus outdoors for a few hours a day. Place it in an area out of the wind and in full shade. After a week of bringing it indoors overnight and leaving it out for longer and longer each day, you can leave it in full to partial shade, preferably in a spot where the sun is filtered through the leaves of trees. If it's getting too much sun, the plant will let you know, either by going limp or by turning slightly red along the fleshy stems. Also note that all parts of the plant are toxic, so place the plant out of reach of pets and children.
Although Christmas cactuses like it on the dry side, you need to check outdoor plants more frequently to see if they need water. Whenever the top 1 inch of soil in the pot is dry to the touch, water the plant. Fertilizer throughout the spring and summer helps the plant put on new growth that will develop into growing points. Clemson Cooperative Extension recommends fertilizing monthly with a 20-20-20 product that includes trace elements at one-half the label recommended amount. A standard label recommendation of 1 teaspoon of fertilizer diluted in 1 gallon of water, would mean you only need to mix 1/2 teaspoon with the same amount of water. Check the label as rates vary among brands. Supplement the plant's magnesium and increase bud production with 1 teaspoon of Epsom salts dissolved in 1 gallon of water two weeks after fertilizing each month through late summer.
4. Moving Back Indoors
Christmas cactuses need 14 hours of uninterrupted dark each night as temperatures start to drop in fall to set buds to bloom in December. Begin moving the plant indoors before nighttime temperatures drop below 50 F, bringing it indoors overnight and taking it back out for a decreasing number of hours over a week. A streetlight or porch light on for a couple of hours each night can keep the plant from setting buds, so even if temperatures never drop below 50 F, you might want to bring the plant in to a room that gets bright, filtered light during the day, but is kept dark at night. Some people consign their plants to a closet overnight -- just don't forget to pull it out each day. Once you see buds, light and dark doesn't matter, just keep the temperature between 50 and 90 F to prevent bud drop.