The secret to getting a Christmas cactus to bloom: temperature and light

To bloom or not to bloom, that is the question many Christmas cactus owners are asking themselves.

During the holidays, the stores are filled with acres of blooming Christmas cacti. They flower brightly with blooms in red, pink, yellow, orange, white or purple. The average gardener can’t keep their hands from clasping one or more in exotic colors and rushing to the cash register.

But at some point, reality intrudes and you not only want to keep it alive, you would like to have it bloom in future years. Why, you might even be leaving a giant, magnificent Christmas cactus to your heirs.

Christmas cactus
Christmas cactus. Photo credit: Bodie Pennisi, Univ. of Georgia, Bugwood.org

Christmas cactus (Schlumbergera truncata) is also known as Thanksgiving cactus, holiday cactus or crab cactus. The crab name refers to the leaf-shaped stem segments that have curved, pointed teeth or claws along the edges. The Easter cactus (Schlumbergera buckleyi) has rounded edges on its leaf segments. They all originated in southeast coastal Brazil in shady, humid forests. They are classified as epiphytes because they live above the ground in the trees, in areas where branches meet and decomposing fallen leaves and mosses collect.

Even though this plant bears the name of cactus, the care that it requires has nothing to do with its desert relatives. It is classified as a forest cactus. Its needs trace directly to its origins. Christmas cactus grows best when it is “pot bound.” That means leaving it in a small container for as long as possible and then moving up to just a slightly larger pot. They prefer a rich, organic potting mix and should not be allowed to dry out. Increase the amount of water when the plant is blooming. They prefer bright, indirect light. Full sun can cause the leaf segments to turn dark red as the plants begin to burn.

The “trick” to getting Christmas cactus to bloom in the following years after purchase comes down to two things: light and temperature. These two are the keys to the flower kingdom. Christmas cacti produce flowers in a cool, environment-short day cycle. To initiate the production of flower buds, there needs to be at least eight days of 16 hours of dark and eight hours of light each day. Wherever the plant is placed, do not turn on the lights at night, even for a short period of time. That breaks the dark cycle required. The temperature should be around 61 degrees. Avoid placing the plant where it receives either cold or hot air drafts.

Placing the Christmas cactus on the window sill in a cool room and not turning on the lights is all that’s needed. If the plant was in a lighted room, often the side to the window develops buds, but the lighted side of the plant does not. If the plant sets flower buds and then they fall off, it usually has to do with either receiving too much or not enough water or lack of air humidity. The good news is that Christmas cacti are considered relatively easy to get to bloom again if their temperature and light requirements are met.

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