Plant care guide
Christmas Cactus Not Blooming: Long Nights and Cool Temps
Updated
Why is my Christmas cactus not blooming?
A Christmas cactus that won't bloom has usually missed its autumn cue: about six weeks of long, unbroken nights with cool temperatures. A lamp in the evening or a warm room is the most common reason buds never form.
What to do first
From mid-September, give the plant 14 hours of complete darkness each night and nights of 13–18 °C (55–65 °F) for about six weeks. Keep it in bright light by day and stop fertilizing in late summer.
A healthy Christmas cactus that refuses to flower is rarely sick. It is missing a signal. Holiday cacti are short-day plants: they grow leaves in summer and form flower buds only when autumn nights get long and cool.
NC State Extension puts it bluntly in its Schlumbergera profile: if your plant does not flower, it is probably getting artificial light when it needs total darkness. Start with the night, then check temperature, stem maturity and feeding.
Which holiday cactus do you have?
Iowa State University Extension notes that most plants sold as “Christmas cactus” are actually Thanksgiving cactus (Schlumbergera truncata) or hybrids. Thanksgiving cactus has pointed teeth on its stem segments; true Christmas cactus (S. × buckleyi) has rounded, scalloped edges. Both need the same autumn treatment. The Easter cactus has a different, longer cooling schedule and is not covered here.
Check the four causes
1. Light at night
Buds form only after a run of long, unbroken nights. Clemson Cooperative Extension says street lights, car lights or indoor lighting can disrupt the dark period. A living room where lamps go on at dusk is enough to stop bud set.
The extension guides give slightly different minimums:
| Source | Uninterrupted darkness | How long |
|---|---|---|
| Iowa State | 14–16 hours (some cultivars bloom with 12) | From late summer |
| Clemson | 14 hours or more, from mid-September | At least 6 weeks |
| NC State | At least 13 hours | Mid-September to mid-November |
| Minnesota | At least 12 hours, with nights of 16–18 °C (60–65 °F) | About 6 weeks |
Aim for 14 hours. That satisfies every source on the list.
2. A warm room
Temperature matters as much as darkness. Iowa State says temperatures above 21 °C (70 °F) prevent flowering even with short days. The University of Minnesota says plants are unlikely to bloom with nights above 18 °C (65 °F). Both recommend nights of roughly 13–18 °C (55–65 °F).
Cool nights can even replace darkness. Minnesota, Illinois and Iowa State Extension all say nights near 13 °C (55 °F) can set buds regardless of day length. Don’t go colder: Clemson and Illinois warn that buds may drop at 10 °C (50 °F) or below.
3. Stems too young to flower
Flowers form at the tips of mature stem segments. Clemson recommends “leveling” at the end of September: pinch off any tip segments shorter than 1 cm (0.4 inch). These short segments won’t set buds, but the mature segment behind them will.
Late pruning removes the tips that would have flowered. UF/IFAS Extension advises making the last pruning in late spring.
4. Feeding and light by day
Iowa State’s houseplant diagnosis guide lists low light and too little fertilizer in spring and summer as reasons houseplants don’t flower. Clemson advises feeding monthly from spring through summer, then stopping in late summer for better bud set. Minnesota suggests switching to a half-strength, low-nitrogen fertilizer in autumn.
What to do this autumn
- Mid-September: move the plant to a room where lights stay off at night, such as a spare bedroom. Illinois Extension suggests an unused bedroom or basement. Keep it in bright, indirect light by day.
- Or use a closet. UF/IFAS suggests a dark closet from 5 p.m. to 8 a.m. each day for six weeks. Plants treated this way bloom in about ten weeks.
- Keep nights cool, around 13–18 °C (55–65 °F), and away from heat vents.
- Level the stems at the end of September by pinching off very short tip segments.
- Water evenly. Clemson says the mix must stay evenly moist once buds have set, to prevent bud drop.
- Stop the treatment once buds show. Clemson notes buds are normally visible in 3 to 4 weeks, and night length no longer matters once they have set.
Before next year
Clemson and Minnesota both say holiday cacti flower best when somewhat pot-bound, so repot only every three years or so, in spring. Iowa State advises keeping plants on the dry side when not in flower, because overwatering causes limp growth and root rot. Pinching stems in June, as Clemson and Illinois suggest, gives more branch tips for flowers.
If the plant is limp or rotting, fix the roots first: a stressed plant will not bloom well. The Christmas cactus hub covers general care, and our houseplant root rot guide explains the root check. The ASPCA lists Schlumbergera as non-toxic to cats and dogs.
Related guides
Other christmas cactus problems we cover: bud drop, limp leaves.
References
- Iowa State University Extension: All About Holiday Cacti
- Clemson Cooperative Extension: Thanksgiving & Christmas Cacti
- University of Minnesota Extension: Holiday cacti
- NC State Extension Gardener Plant Toolbox: Schlumbergera
- University of Illinois Extension: How to identify and care for holiday cacti and get them to rebloom
- UF/IFAS Gardening Solutions: Christmas Cactus Preparation
- Iowa State University Extension: Diagnosing Houseplant Problems from Improper Environmental Conditions
- ASPCA: Christmas Cactus
How this guide was put together: Iowa State University, Clemson, University of Minnesota, NC State, University of Illinois and UF/IFAS Extension guidance.