Christmas cactus care: blooms, water and bud drop

Light

Bright, indirect light is the consensus. NC State calls the genus intolerant of direct sun, UF/IFAS suggests a spot within six feet of a south, east or west window, and Clemson says holiday cacti grow best in light shade. Strong summer sun washes the segments pale and yellow, Clemson warns, which is the cue to pull the pot back from the glass.

Fall changes the rules. Clemson notes that full sunlight is beneficial during fall and winter, when the sun is weaker, and bright days are one of the conditions bud set requires. The other is darkness: Clemson calls for 14 hours or more of uninterrupted darkness each night from about mid-September for at least six weeks, and warns that as little as 2 hours of interrupted lighting can inhibit bud set. NC State gives at least 13 hours and UF/IFAS at least 12. A street lamp, passing headlights or a reading lamp left on in the evening can be enough to cancel the show.

Water

Water when the top inch of soil feels dry, UF/IFAS advises, and Clemson says to water once the growing medium is dry to the touch. Unlike desert cacti, this one should never dry out completely in spring and summer, according to Clemson's guide to rainforest cacti, although it tolerates being slightly underwatered better than being soggy. NC State offers a rough rhythm for the genus: about every 1 to 2 weeks, or when the soil is nearly dry. Always tip out the saucer afterward.

Autumn is when watering gets subtle. Clemson's indoor cactus guide recommends reducing water around the end of September as part of the rest period that helps set buds, and NC State says to cut back in mid-September and again after flowering. Once buds have formed, though, Clemson's holiday cactus factsheet says the medium must be kept evenly moist, because drying out is one of the triggers for buds falling before they open.

Through the dark days of winter, keep the soil from becoming waterlogged without letting it go bone dry, Clemson advises. Overwatering is the main disease risk: root rot, which NC State notes can also turn the stems mushy.

Soil and pH

Clemson suggests 60 to 80 percent potting soil combined with 20 to 40 percent perlite, and stresses drainage and aeration, because epiphytic cacti do not grow well in heavy, wet mixes. Its indoor cactus guide gives a richer alternative of two parts peat moss, one part garden soil and one part sand. NC State describes an airy medium of peat moss, sand and perlite. A desert cactus mix on its own is too lean; Clemson notes that rainforest cacti need more organic matter than desert types.

Humidity

This is the one cactus that likes humid air. Clemson's guide says rainforest cacti prefer at least 50 percent humidity but will tolerate less, and suggests misting may help indoors; NC State lists high humidity as a preference. Low humidity is one of the conditions NC State links to bud drop, so a pebble tray or a humidifier in the weeks before bloom is worth setting up in a heated home.

Temperature

Clemson puts ideal growth at 70 to 80°F from April to September, and NC State agrees. In autumn, cooler nights help: NC State recommends night temperatures of 55 to 65°F, and Clemson says plants kept at night temperatures between 50 and 59°F will set buds regardless of day length, though growth slows and buds may drop at 50°F. Clemson advises holding fall temperatures as close to 68°F as possible for maximum flowering, never letting them rise above 90°F once buds are set, and bringing plants indoors before nights fall below 50°F (10°C). At 68°F, flowering can last 7 to 8 weeks.

Fertilizer

Clemson recommends feeding monthly at half strength from late winter or early spring, when new growth starts, through the summer, using a soluble fertilizer such as 20-10-20 or 20-20-20 with trace elements. UF/IFAS gives every one to two months from April to September. Holiday cacti need more magnesium than many plants, so Clemson also suggests Epsom salts (magnesium sulfate) at 1 teaspoon per gallon of water monthly during the growing season, never in the same week as the regular fertilizer. Stop all feeding in late summer to favor bud formation; Clemson's indoor cactus guide says to resume after flowering.

Work out the dose for your watering can with the fertilizer dilution calculator →

Repotting

Christmas cacti flower best when somewhat pot-bound, and Clemson says repotting is needed only about once every three years, ideally in spring. UF/IFAS warns against choosing a pot that is too large. Go up just one size, use the airy mix described above, and never repot a plant carrying buds or flowers; Clemson's general repotting guidance says not to repot plants that are beginning to flower.

• Roots fill the pot and push out of the drainage hole
• The mix breaks down and stays wet for days
• The plant dries out unusually fast between waterings

Propagation

Clemson calls holiday cacti easy to propagate from cuttings taken in May or June. Twist off sections of 3 to 5 segments, let the cut ends callus in shade for a day or two, then set them about one inch deep in well-drained potting soil, three cuttings to a 4-inch pot or five to a 6-inch pot. A clear plastic bag over the pot holds humidity high, and roots form in three to eight weeks in bright, indirect light. Early June is also when Clemson suggests pinching the stems back to encourage branching, so the trimmings can become new plants. NC State adds grafting as a second method.

Methods: Stem cuttings of 3 to 5 segments, Grafting · Best season: may or june.

Common problems

Bud drop is the classic disappointment. Clemson traces it to an excessive number of buds, a sudden change in temperature or light, or a medium that dried out, and UF/IFAS adds drafts and heat sources such as vents and fireplaces. A plant that never blooms is almost always getting light during its long nights. Root rot from overwatering is the major disease, and Clemson lists mealybugs, soft brown scale, red spider mites, aphids and fungus gnats as the pests. Segments that yellow and fall usually mean the plant was kept too dry or given too much sun, according to Clemson's cactus guide.

Not sure which one it is? Try the plant problem diagnosis tool →

Is the Christmas cactus toxic to cats and dogs?

The ASPCA lists the Christmas cactus as non-toxic to cats, dogs and horses; its entry uses the name Schlumbergera bridgesii, an older label for the plant. The ASPCA's shrimp cactus entry, Schlumbergera russelliana, one of the hybrid's parents, is also non-toxic. NC State likewise describes the Christmas cactus as non-toxic and safe in homes with pets or children. Non-toxic does not mean the segments are food, and a chewed plant is slow to fill back in, so a high shelf still helps. If a pet seems unwell after eating any plant, call your veterinarian or the ASPCA Animal Poison Control Center.

Check any other plant against the ASPCA lists →