To get a Christmas cactus to bloom, give it long, uninterrupted nights and cooler air for roughly four to six weeks, then leave it alone once buds appear. Extension sources put the darkness at about 12 to 16 hours a night (they differ on the exact number) and night temperatures at about 55 to 65°F. When buds drop, the cause is usually one of a short list: a sudden change, a draft or heat source, soil that dried out or stayed soggy, or moving the plant after buds formed.
This plan applies to the Christmas, Thanksgiving, and Easter cacti sold as "holiday cactus." If you are not sure which one you have, our guide to how to tell them apart takes about two minutes.
What Tells a Holiday Cactus to Set Buds
Holiday cacti are short-day plants. They start making flower buds when nights get long and, in most sources, cooler. The extension guidance we reviewed agrees on the idea but gives different numbers:
- Darkness: at least 12 hours of continuous darkness (University of Florida and University of Illinois Extension), 12 to 14 hours (Penn State Extension), or 14 to 16 hours of uninterrupted darkness (Iowa State University Extension).
- Night temperature: 55 to 65°F is the range Penn State and University of Illinois Extension give. University of Wisconsin Extension says cool nights of 55 to 60°F, combined with the natural fall day length, will induce flowering.
- Time: about six weeks of short days for Christmas and Thanksgiving cactus, according to Penn State Extension, and eight to twelve weeks for Easter cactus. University of Illinois Extension says five to six weeks.
Because the sources disagree, treat the numbers as a range rather than a rule. The common thread is long nights that are really dark, nights that are cool rather than warm, and steady conditions while buds form.
A Simple Bud-Set Plan
- Pick a spot that is dark at night. University of Florida Extension advises keeping the plant away from artificial light at night from October through December if you want it to bloom for the holidays. Penn State Extension notes that interrupting the dark period for too long, which it puts at two hours or more, can prevent buds from forming. A spare room or a dim corner that nobody switches a lamp on in often works.
- Keep nights cool, not cold. Aim for roughly 55 to 65°F at night and keep the plant away from heat vents and fireplaces. University of Wisconsin Extension notes that holiday cacti cannot tolerate frost.
- Give it bright, indirect light by day. Every source recommends bright indirect light. Direct, hot sun is the thing to avoid. Our guide to bright indirect light shows how to test a spot.
- Water by the soil, not the calendar. University of Florida Extension suggests watering when the upper inch of soil feels dry and not letting the plant get too dry between waterings. Once buds are forming, Iowa State and Penn State Extension both say to keep the soil evenly moist without overwatering. University of Wisconsin Extension notes that some growers ease off slightly in August and September to harden the stems, then resume normal watering when buds begin to swell. Our guide to how often to water houseplants explains the soil check.
- Hold off on repotting and heavy feeding. University of Florida Extension says holiday cacti prefer to be a little root-bound, so avoid a pot that is too large. Penn State Extension suggests feeding monthly in spring and summer and reducing feeding in fall and winter.
- Do not move it once buds appear. University of Wisconsin Extension warns that moving the plant to a place with radically different light or temperature after buds start to form may cause them to stop developing and drop.
If you start now, the plan above puts bud formation roughly four to six weeks out. Treat that as an estimate: it depends on your room, your plant, and which type you have.
Why Buds Drop, and What to Check
Bud drop is common and usually fixable on the next round. The extension sources we read name these causes:
- Sudden changes in temperature, light, or humidity (Iowa State and University of Illinois Extension).
- Drafts or heat sources such as vents, fireplaces, and televisions (University of Florida Extension).
- A room that is too warm while buds are forming (University of Illinois Extension).
- Too much water or too little. Iowa State Extension lists both excessive watering and letting the soil dry out excessively, and Penn State notes that if conditions dry out too much while in flower, buds or flowers can drop.
- Low humidity or too little light (University of Illinois Extension).
- Moving the plant during bud development (Iowa State and University of Wisconsin Extension).
To narrow it down, think about what changed in the week before the buds fell. A new spot, a cold window, a heating vent that came on, a missed watering, or a wet saucer is usually the answer. If humidity is a suspect, our guide to increasing humidity for tropical houseplants compares the options.
If It Still Will Not Bloom
- Nights too warm. University of Illinois Extension and Penn State both tie flowering to cooler nights. A heated living room that stays in the 70s at night works against bud set.
- Light at night. A hallway light, a lamp, or a screen can break up the long night.
- Not enough bright light by day. University of Illinois Extension notes that too little light can cause problems, while too much sun can turn the plant pale or sunburnt.
- Wrong season for the type. Easter cactus needs a longer short-day period and blooms in spring, not at the holidays.
- Not enough time. Buds take weeks to form and more weeks to open.
After the Blooms
Iowa State Extension suggests moving the plant to a cooler spot and watering less after flowering, then returning to normal care and monthly feeding in the growing season. Repot only when it has completely outgrown its container.
Is a Holiday Cactus Safe for Pets?
The ASPCA lists Christmas cactus (Schlumbergera bridgesii) as non-toxic to dogs, cats, and horses. It also notes that eating any plant material may cause vomiting and stomach upset in dogs and cats, so keep plants out of reach if your pet chews. Confirm the botanical name of the plant you own, since the ASPCA entry we read does not list Thanksgiving cactus by name.
From the Greenhouse Bench
Growers do not leave bloom to chance. University of Wisconsin Extension describes controlling flowering by regulating light to a short 10-hour day for about four weeks, after which buds begin to appear. At home, the same lever is the night. Our Holiday Cactus (Schlumbergera) comes in 4-inch pots in several colors. The listing does not specify which species it is, so we suggest checking the stem edges with our identification guide. You can see what is available on our holiday cactus page or browse our holiday and spring cacti.
Frequently Asked Questions
How long does a Christmas cactus take to bloom?
Penn State Extension says about six weeks of short days for Christmas and Thanksgiving cactus, and eight to twelve weeks for Easter cactus. University of Illinois Extension gives five to six weeks. Flowers then take additional time to open.
Can I use a grow light on a Christmas cactus?
You can use one for daytime light, but University of Florida Extension advises keeping the plant away from artificial light at night. If you use a light, put it on a timer so the plant still gets a long, uninterrupted night.
Should I fertilize while it has buds?
Penn State Extension recommends feeding monthly in spring and summer and reducing feeding during the fall and winter. Most of the focus during bud set should be on steady conditions.
Should I put it in a closet at night?
You can, as long as the plant stays cool and gets bright light during the day. The goal is simply long, uninterrupted darkness, so any spot that is dark at night will work.
Why do my buds fall off after I bring it home?
A new home usually means a change in light, temperature, and humidity, and sources list sudden changes among the top causes of bud drop. Pick a spot, keep it there, and avoid drafts and vents.
The Short Version
Long dark nights, cooler air, steady moisture, and no moving once buds show. If you are not sure what type you have, start with our guide to Christmas, Thanksgiving, and Easter cactus.
Sources: Iowa State University Extension: All About Holiday Cacti, University of Illinois Extension, University of Wisconsin Extension: Holiday Cactus, Penn State Extension: Bring on the Blooms with Holiday Cacti, UF/IFAS Gardening Solutions, and the ASPCA Christmas cactus entry. Photo: Cameron Arksey on Unsplash.