To flower, a Christmas cactus needs long, cool, dark nights in fall.
Light and water keep the plant growing; long nights and cool air set the buds.
A gift plant often arrives covered in flowers, so the first year feels easy. The second year, a healthy green plant with no buds is a puzzle.
Is it a Christmas cactus or a Thanksgiving cactus?
The two look alike and are often sold under one name.
The University of Georgia’s Cooperative Extension office in Paulding County, part of the university’s public gardening advice service, says Thanksgiving cacti are often sold as Christmas cacti.
The easiest check is the edge of the flat stem segments.
- Thanksgiving cactus: jagged, saw-toothed edges. It flowers near Thanksgiving, about a month before the Christmas type.
- Christmas cactus: smooth, rounded edges. It flowers about a month later.
Both need the same care; the practical difference is when they flower.
A plant with rounded edges that blooms early is probably getting cool, long nights sooner than you think.
Light and water the rest of the year
The University of Florida’s IFAS Extension, which answers home gardeners’ questions, asks for bright, indirect light within six feet of a south-, east- or west-facing window.
Water when the upper inch of soil feels dry. The New York Botanical Garden’s plant information service waits until the top half is completely dry.
Let the top of the soil dry first, then water well and empty the saucer after 15 minutes.
The stems and roots can rot if the soil stays wet, so the pot needs a drainage hole and a loose, well-drained mix.
This plant prefers to be a bit root-bound. A pot only slightly larger than the roots is enough.
If you want more plants like this one, there are other forgiving houseplants for a calm home.
The fall nights that set buds
In fall the plant sets buds with long, dark nights, cool nights, or both, and lamp light at night works against it.
Give it 12 to 14 hours of uninterrupted darkness every night, starting about the middle of September, for at least six weeks. The exact figure depends on the guide.
A black cloth over the plant from 6 pm to 7 am is one way to do it.
Cool nights help. Night temperatures of 50 to 59 degrees F set buds whatever the day length, though buds may drop at 50 degrees F.
Keep lamps off near the plant at night from October through December. As little as two hours of interrupted light can stop buds from forming.
So a room you use in the evening is a poor spot in September and October. A spare room with a window and no evening lamps works better.
The plant can stay outdoors in fall, then come inside just before freezing is a threat. It should not stay out if nights fall below 50 degrees F.
Why buds drop
Christmas cactus can be prone to bud drop, so avoid extreme changes. Keep it away from drafts and heat sources such as vents, fireplaces and televisions.
Moving the plant while buds are forming can also make them drop.
Once buds show, pick a spot and leave the plant there.
Two more causes: after buds set, the soil needs to stay evenly moist, and temperatures above 90 degrees F can make buds fall.
Poinsettias also start flowering as days grow shorter; poinsettia care after the holidays follows the same long-night idea.
After the flowers fade: a calendar
Here is a simple plan from one fall to the next.
- Mid-September: start the long nights.
- October to December: keep lamps off near the plant at night. Buds should be visible in three to four weeks.
- While buds form and open: keep the soil evenly moist and do not move the pot.
- After flowering: remove spent flowers and stem tips to get more branching.
- Late winter to summer: feed during the growing season, every one to two months from April to September.
- Spring: repot only about every three years.
- Early June: pinch back stems to encourage branching. Do not prune beyond mid-summer.
One guide starts monthly feeding in late winter and stops in late summer.
The plant does not need repotting or feeding in fall. The only fall trim is removing very short stem tips at the end of September.
Cuttings with two or three jointed sections root easily. Set them in sterile, well-drained mix and keep them moist in bright, indirect light until new growth appears.
Next year, write the middle of September on your calendar and start the long nights that day, keeping lamps away from the plant after dark.