Q: I was given a Christmas cactus last year and I loved it. I put it outside on my shady porch and it has thrived. It has been full of buds. With these cold nights, I decided to bring it inside. Now the plant is losing its buds, one flower at a time. It seems like every time I turn around, more have fallen off. What can I do?
A: As soon as we hear the word cactus we usually assume the plant must like a hot, dry environment. However, Christmas cactus, Schlumbergera bridgesii, is a native of the rain forests of Brazil. These plants typically are found growing in the canopy of shade trees, which is why the plant adapted so well on your back porch, protected from direct light. I suspect the reason for the bud drop is the extreme temperature change from the outside to indoors. Moving them back outside might produce an additional shock so I would not recommend it.
Christmas cactus can tolerate summer temperatures near the 80s but it will show some adverse damage when temperatures drop below 50. This moderate temperature range preference is one of the reasons why many people opt to keep it indoors. You could keep it outside during the winter and protect it with a light covering when temperatures drop below 50. Christmas cactus does not have true leaves. The flat, green, leaf-like structures holding the flower are actually specialized stems called phylloclades. If they are exposed to too much direct sunlight, they turn pale green.
You can alternate fertilizer application with a small amount of Epsom salts – magnesium sulfate (1 teaspoon per gallon of water). This plant can tolerate a dry soil but during budding and flowering, it is best to keep the soil moist but not wet. Pinch back the stems (phylloclades) in early June to promote branching. Remove the short, terminal stems in September to encourage flower bud formation. Flowers will only develop on mature stems. Keep the plants away from direct lighting in the evening hours as this will discourage flower.