When to Repot and Propagate Christmas Cactus (and Start Bloom Treatment)

Repot in late winter or early spring

Penn State Extension says the best time to repot is late winter or early spring, once flowering is completely over. Never repot a plant in bloom. Repotting is a rarely needed job. Penn State suggests every 3 to 4 years, and UW-Madison Extension says at least every 4 to 5, because the peat in most mixes breaks down and stops draining.

Signs it is time:

• Roots grow out of the drainage holes.
• The plant looks “tired,” in Penn State’s word, and puts out little new growth.
• It dries out and wilts much sooner after watering than it used to.
• Younger stems shrivel even though the mix stays moist, or segments drop off. UW-Madison treats these as signs of root loss: unpot the plant and check the roots right away, whatever the season.

Pot and mix

Go up only slightly in pot size. The plant blooms best a bit root-bound. Use a fast-draining, airy mix, such as a packaged succulent mix, or peat with plenty of perlite. Remove most of the old mix and check the roots. Set the root ball about an inch below the rim, and water moderately. Keep the plant in light shade for 2 to 3 days. UW-Madison advises watering somewhat less than usual for about a month while new roots form.

Propagate from late spring through summer

Christmas cactus roots from cuttings year-round, but UW-Madison reports the best rooting from late spring through summer. Twist off a piece with two to five segments. Let it dry in the shade for 2 to 3 days, then set it in moist perlite or a well-drained mix. Roots form in about 2 to 3 weeks according to UW-Madison, or 3 to 8 weeks according to Penn State, which suggests rooting hormone and a plastic bag over the pot to hold humidity.

Do any pruning by midsummer at the latest. UF/IFAS warns against pruning past midsummer, because late cuts remove the stem tips that would carry this year’s flowers.

Move it outdoors once nights stay above 55°F

A summer in light shade outdoors suits this plant, but wait well past the last frost. UW-Madison puts its minimum at 55 to 60°F. That is warmer than the 50°F night rule Illinois Extension uses for houseplants in general, so hold off until nights stay above about 55°F. Hang it from a tree branch or set it on a shaded porch, and keep it off the ground away from slugs.

Fall: the bloom window

Buds form in response to long nights, cool nights or both. Sources give slightly different recipes:

• NC State: from mid-September, bright days, nights of 55 to 65°F, and at least 13 hours of uninterrupted darkness every night.
• Purdue: start around mid-October with about 12 hours of darkness, roughly 8 p.m. to 8 a.m. in a closet, for 6 to 8 weeks or until buds show. Alternatively, nights of 50 to 55°F trigger buds without the dark treatment if they begin by early November.
• UW-Madison: cool nights of 55 to 60°F with natural fall day length are enough. If the plant stays above 60°F, limit it to 10 hours of light a day for about 4 weeks, using a dark room or a cover.
• UF/IFAS: keep it away from artificial light at night from October through December.

Ordinary room lighting in the evening is enough to interrupt the dark period. NC State says artificial light in fall is the usual reason a plant fails to bloom. A plant summering outdoors gets fall’s lengthening nights and cooler temperatures naturally. Bring it in once nights fall toward 55°F, since it can’t tolerate frost. Indoors, a cool room that is not lit at night does the same job.

During this period, NC State suggests watering a little less from mid-September, and Penn State warns against heavy feeding while buds develop.

Once buds appear, you can stop the treatment and return the plant to normal room conditions. Choose a spot with similar light and temperature, though. UW-Madison notes that a sudden, large change can make the buds abort. Each cultivar responds a little differently, and a Thanksgiving cactus naturally blooms weeks earlier, so it can take a season or two to learn your plant’s timing.

Bring it in before nights drop below 55°F

Bring it indoors before nights fall below about 55°F, the bottom of UW-Madison’s range, and well before any frost. Purdue’s 50 to 55°F bud trigger means nights near that line help set buds, but don’t leave the plant out colder than that. Purdue suggests easing the transition by bringing the plant inside for a few more hours each day. Illinois Extension advises inspecting houseplants for pests before bringing them inside. Look along the stem joints and undersides for mealybugs, scale and spider mites, and check the pot for slugs.