I have just purchased a hot pink Christmas cactus. What should I do throughout next year to ensure that it blooms again in time for next Christmas?—AW, Pearisburg, Va.
Answer: Christmas cactuses (Schlumbergera ×buckleyi) are very easy to keep and may live so long that they become family heirlooms. There are now more than 200 named cultivars, blooming in all shades of red, pink, orange, yellow, and white.
Although of garden origin, these plants’ ancestors come from southeastern Brazil. They are epiphytic plants, and in the wild they root in decaying humus and leaf debris in crevices and tree crotches. It follows that Christmas cactuses need adequate moisture, perfect drainage, and indirect bright light. A northern or eastern window is good. Southern and western windows may be too sunny, but if you can adjust the slats of a blind to permit just a little direct sunlight to strike the plant, it should be fine. You can also put the plant outside for the summer, in light or dappled shade.
Allow the soil to dry slightly in between waterings. The leaves will wrinkle and yellow if the plant is kept too dry. Fertilize monthly during spring and summer. These plants like to be a bit pot bound; should you decide to repot, step up only one size.
As with the poinsettia, blooming is stimulated by short days—or, more accurately, by long nights. Cooler temperatures also play a role. Florists provide artificial periods of darkness to get their plants to bloom on cue, but seasonal changes in late summer and fall usually result in flower bud formation, especially if the nighttime temperature is 55–60°F. Once the plant has formed buds, do not relocate it or dramatically change its conditions. Otherwise bud drop may occur.
All of this explains why that Christmas cactus kept in the same place by an elderly relative who goes to bed with the sun and does not spend much money on heating the house has always bloomed so beautifully and so predictably.