How to Get a Christmas Cactus to Bloom, and Keep the Buds

What sets the buds: long nights and cool nights

Holiday cacti are short-day plants. Minnesota Extension says they form buds as the hours of daylight fall toward winter, and that cool nights are required too. Iowa State Extension says day length and temperature matter equally, and that a room that stays warm prevents flowering even with long nights.

Either one can do the job, the sources say. Minnesota, Purdue, Illinois and Iowa State all say that a plant kept in a cool room at night through fall will set buds whatever the day length, and Minnesota says that takes about 5 to 6 weeks. In a warmer room, the long dark nights have to do the work. NC State Extension’s Beaufort County office calls using both together the foolproof method.

Cool does not mean cold. Clemson Extension says buds may drop if the nights get too cold, and Illinois says the same. Once the buds have set, Clemson and Illinois both say day length no longer affects flowering.

More on Christmas cacti

• Christmas cactus care — light, water, feeding, leaf color, repotting, and when a pot goes outside in your zone
• Christmas vs Thanksgiving Cactus: How to Tell Them Apart
• How to Get a Christmas Cactus to Bloom, and Keep the Buds — this page
• Christmas Cactus Propagation: Rooting Cuttings Step by Step
• ZIP code zone finder — your exact USDA zone, to read the tables on these pages against

How long the nights need to be, by source

The dark must not be broken. Clemson and Illinois both say as little as 2 hours of light in the night can stop buds forming, and Clemson names street lights, car lights and indoor lamps. NC State says a plant that does not flower is probably getting artificial light when it needs darkness. A closet, an unused bedroom or a basement works (Purdue, Iowa State, Illinois), or a cover of black plastic (Wisconsin). Bring it out to bright light each day: Iowa State and NC State both want bright light by day.

A fall calendar for Thanksgiving or Christmas

Thanksgiving here is the US holiday, the fourth Thursday of November. Clemson Extension says a Thanksgiving cactus left to ordinary fall nights flowers near Thanksgiving, and a Christmas cactus about a month later; check which one you have before you plan. Then, counting back:

• June. Clemson and Illinois Extension pinch the stems back in early June, so the plant branches and has more tips to flower from. UF/IFAS says not to prune beyond mid-summer.
• Late summer. Clemson stops fertilizing for more buds in fall; Minnesota switches to a fertilizer low in nitrogen and high in phosphorus and potassium while the buds form.
• Mid-September. NC State and Clemson start the long nights. At the end of September, Clemson “levels” the plant, pinching off any tip segment shorter than about 1 cm (0.4 inch), because a segment that young will not set a bud and the bud forms on the mature one behind it.
• Late September or October. Cornell Cooperative Extension of St. Lawrence County starts 8 to 10 weeks before Christmas, in a spot with natural light and no lamps after dusk.
• Mid-October. Purdue Extension starts the dark treatment for full bloom by the holidays, and says a cool-room treatment started by early November also works.
• When buds show. Stop moving it. Iowa State waits until the first flowers open before putting the plant on display.

To bloom later, keep it warm and lit for longer. UGA’s Paulding County office says the earlier the cool nights and long dark start, the sooner the plant flowers, and suggests a warm, well-lit room you use in the evening if you want blooms later in the season. University of Wisconsin–Madison Extension says each cultivar responds a little differently, so hitting an exact date may take a few years of trying.

The easy way: leave it outside until just before frost

Minnesota Extension says to leave the plant outdoors in a protected spot until just before frost danger, so the shorter days and cooler nights start the buds, and UGA’s Paulding County office says the same. Illinois and Clemson bring it in sooner, once fall nights turn cool. For your area’s first fall freeze, see the “Bring indoors before” column on the Christmas cactus care page, which reads it from NOAA records for your zone, and treat it as the latest date, not the safest.

Water steadily, and do not dry it out

Older advice says to dry the plant down in early fall. The University of Arkansas Cooperative Extension Service says researchers who tested it found the opposite: plants kept evenly moist averaged 2.5 flowers per segment, and plants given a dry-down 1.5. Clemson keeps the mix evenly moist once the buds have set, and Iowa State keeps it evenly moist while the plant buds and flowers.

University of Wisconsin–Madison Extension reports that some growers cut watering slightly in August and September to harden the stems that will carry the flowers, and go back to normal once the buds swell. If you try it, it is a slight cut, not a dry pot.

Why it is not blooming

• Light at night. NC State, Clemson and Iowa State all put this first. Lamps, a kitchen light, a TV, street lights or car headlights can be enough.
• A room that stays warm. Minnesota Extension says a plant kept in warm nights is unlikely to bloom at all; Iowa State says warmth prevents flowering even with long nights.
• Too little light by day. Purdue Extension says the plant adapts to low light but flowers more with more light.
• Short of nutrients. Minnesota lists this, and feeds at half strength in fall with a low-nitrogen, high-phosphorus and potassium fertilizer.
• Pruned too late. UF/IFAS says not to prune beyond mid-summer, and UC Master Gardeners of Sacramento County prune before the buds set, usually in late summer or early September.
• Struggling roots. University of Wisconsin–Madison Extension lists fewer flower buds and buds that abort among the signs of a root system failing in old, broken-down potting mix. The care page covers repotting.
• It already bloomed. University of Wisconsin–Madison Extension says a plant in full bloom at Thanksgiving will be done blooming by Christmas.

Why the buds fall off

Once the buds start, Minnesota Extension says, these plants do not like to be disturbed. The causes the sources name:

• Moving it. Iowa State and Wisconsin both say not to move a budding plant into a spot with very different light or temperature. Minnesota says if it must go to a warmer room, move it as soon as the buds appear, not later.
• Drafts and heat. Minnesota names drafts, heaters and vents; UF/IFAS vents, fireplaces and televisions; Cornell’s St. Lawrence County office adds wood stoves, sunny south windows that heat up, and leaky doors and windows.
• Water. Soil that dries out (UF/IFAS, Iowa State, Clemson, Illinois) and soil kept too wet (Iowa State, Illinois). Minnesota says water left standing in the saucer can cause bud drop.
• Changes in light, humidity or temperature. Minnesota, NC State and Illinois, which also names low humidity.
• Too many buds. Minnesota and Clemson both say a plant may drop the buds it cannot support. Minnesota calls it self-pruning and says good care is the answer.

A plant bought in bud may drop some as it settles in. UC Master Gardeners of Sacramento County say store plants were grown in ideal greenhouse conditions, so do not be surprised if buds drop at home; the plant adjusts for future years.

While it blooms, and after

Keep it cool to keep the flowers. Purdue and Cornell’s St. Lawrence County office both say a holiday cactus holds its blossoms longer in a cooler spot. University of Wisconsin–Madison Extension says plants bloom for 2 to 3 weeks in an ordinary warm room, and Clemson says flowering can last up to 7 to 8 weeks in the right conditions. Purdue says the plant does not need feeding while in bloom.

After flowering, Minnesota and Iowa State water less often and Minnesota prunes to encourage branching. NC State says a Thanksgiving cactus may bloom a second time as the days lengthen in February.

The Easter cactus works differently

Iowa State Extension says the Easter cactus needs a stricter sequence: long nights for several weeks in fall, then a cooler spell, then longer days, and that it is unlikely to flower if those are not met. NC State says it does not form buds until February or March. How to tell the three apart.

What we could not find

We found no Texas A&M or LSU AgCenter source on holiday cacti that we could read. Southern advice on this page comes from Clemson, UF/IFAS, UGA’s Paulding County office, the University of Arkansas and NC State.