
Photo: Ask Extension, UMD HGIC.
Q: This year, I am again having problems with the flowers on my Christmas Cactus. The plant gets an abundance of flower buds, but most of the ones that flower do not flower completely. Many partially flower, but then start drooping before fully blooming and opening. Also, many of the buds fall off before blooming. I am careful not overwater, and the plant is in a window facing the east.
A: It can be difficult to know for sure what is causing the symptoms, but possibilities include low ambient humidity (these cacti are native to jungle environments, where they grow as epiphytes on the trees like orchids do), temperature fluctuations, under-watering, and possibly exposure to ethylene gas, which can come from a group of ripe fruit and leaks in gas appliances.
When watering, make sure the potting mix is thoroughly rehydrated, and excess water freely drains out of the bottom drain holes. To boost humidity, consider using a humidifier (misting foliage will not be effective).
An east-facing window doesn’t give the plant much light (especially this time of year and if the plant isn’t directly in front of the pane), so if you have an option to grow it in a west- or south-facing window, that may help with growth and vigor overall, even if it may not change much with regards to flower bud dropping. In fact, that may need to wait until after the flowering period, as Iowa State notes that “to avoid flower bud drop, do not move the plant during flower bud development,” though it can be moved once flowers are opening. Michigan State mentions a couple of other causes, such as exposing the plant to light that interrupts its required 13 hours of darkness (a seasonal trigger for flowering) and exposing the plant to temperature swings (drafts), particularly below about 50 degrees. The linked page has more details about the darkness period.
You can also refer to a blog post from a few years back for some further reading: Christmas cacti make lovely gifts and decor by Annette Cormany.

Photo credit: Washington County Master Gardener Wilma Holdway.
By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. Read more by Miri.



