How Do You Care for a Christmas Cactus and Get It to Bloom?

A Christmas cactus blooms after several weeks of long, cool nights, and the rest of the year it needs bright filtered light, soil that dries between waterings and a pot that drains. The University of Minnesota Extension says nights near 55°F can bring blooms in about 5 to 6 weeks, while a plant kept at 60 to 65°F at night needs at least 12 hours of complete darkness every night for about 6 weeks. Plants are unlikely to bloom at all if nights stay above 65°F.

The plant on your windowsill may not be a Christmas cactus. N.C. Cooperative Extension notes that Thanksgiving cacti are often sold as "Christmas cacti," and it gives a simple test: Thanksgiving cactus stem segments have 2 to 4 saw-toothed points along the edges and yellow pollen-bearing anthers, while Christmas cactus segments are rounded and its anthers are purplish brown.

The same guide warns that as little as 2 hours of interrupted lighting will inhibit flower bud set, which is why a cactus sitting next to an evening reading lamp often refuses to flower. This guide covers how to identify your plant, how to set up its bloom season and how to keep it healthy for decades.

What is a Christmas cactus?

A Christmas cactus is a forest cactus in the genus Schlumbergera: a true cactus that grows on tree branches in rainforests rather than in desert sand. N.C. Cooperative Extension describes holiday cacti as native to Brazil, where they grow as epiphytes among tree branches in shady forests.

That background explains most of their care. They want more humidity, softer light and more regular moisture than a desert cactus.

The University of Minnesota Extension lists three holiday cacti: Thanksgiving cactus (Schlumbergera truncata), Christmas cactus (Schlumbergera bridgesii) and Easter cactus (Schlumbergera gaertneri). N.C. Cooperative Extension uses Schlumbergera x buckleyi for the Christmas cactus and notes that the Thanksgiving species was one of its parents, which is why the two look so alike. Both sources agree on the practical point: the holiday names are only general references to when each plant tends to bloom.

These plants can stay in a family for generations. The University of Minnesota Extension says holiday cacti can live over 100 years and are often passed down from generation to generation.

How can you tell a Christmas cactus from a Thanksgiving cactus?

Check the stem segments first. Holiday cacti have no true leaves. The flat green pads are stem segments, and they do the plant's photosynthesis.

• Thanksgiving cactus: each segment has 2 to 4 pointed, saw-toothed projections along the edges. The Sampson County Extension Center compares them to small hooks or claws.

• Christmas cactus: segment edges are smooth and rounded, with slight scalloping.

• Easter cactus: segments are oval with soft, rounded edges and no sharp points.

If the plant is in bloom, look at the anthers, the small pollen-bearing tips in the center of the flower. N.C. Cooperative Extension says Thanksgiving cactus anthers are yellow and Christmas cactus anthers are purplish brown.

Timing is the third clue. Under normal night lengths, N.C. Cooperative Extension says Thanksgiving cacti flower near Thanksgiving, about a month before Christmas cacti. Commercial growers can time both to bloom for holiday sales, so a store plant's first bloom date is not a reliable test.

How do you get a Christmas cactus to bloom?

Holiday cacti are short-day plants. They form flower buds when nights get long and cool in fall, and they need both conditions for several weeks in a row.

Give it long, uninterrupted nights. Extension guides differ slightly on the exact number. The University of Minnesota Extension calls for at least 12 hours of complete darkness each night for about 6 weeks when nights are 60 to 65°F. N.C. Cooperative Extension recommends 14 hours or more of continuous darkness, starting about the middle of September and continuing for at least 6 weeks.

Either way, the dark has to be complete. A spare bedroom, a room nobody uses after sunset or a spot that only gets daylight from a window works better than a family room where lamps go on at dusk.

Keep nights cool. The University of Minnesota Extension recommends daytime temperatures of 65 to 70°F and nights of 55 to 65°F, and notes that at 55°F nights the plant will often bloom in about 5 to 6 weeks regardless of day length.

Use the fall outdoors, carefully. The University of Minnesota Extension suggests leaving holiday cacti outside in a protected spot until just before frost danger, because shorter days and cooler nights signal the plant to set buds. N.C. Cooperative Extension adds a firm limit: do not leave these cacti outside if temperatures will drop below 50°F.

In the Pittsburgh area, NOAA's 1991 to 2020 normals put the median first 32°F night at Pittsburgh International Airport on October 23. The 50°F limit arrives well before frost, so watch the forecast and bring the plant in before the first night in the 40s.

Switch fertilizer in fall. The University of Minnesota Extension recommends a low-nitrogen, higher-phosphorus and potassium fertilizer while buds are forming, such as a 0-15-10 formulation, at half strength.

According to N.C. Cooperative Extension, buds normally become visible 3 to 4 weeks into the long-night period, and once buds are set, day length no longer affects flowering.

Why do Christmas cactus buds fall off before they open?

Buds fall off when the plant's conditions change after they form. The University of Minnesota Extension lists these causes:

• Drafts, or sudden changes in temperature or humidity

• A change in the direction or amount of light the plant receives

• Moving the plant to a warmer room after buds have formed

• Excess water left sitting in the saucer

• More buds than the plant can support, which it sheds on its own

If the plant needs to live in a warmer room during bloom, the University of Minnesota Extension advises moving it there as soon as buds appear rather than later. The Sampson County Extension Center adds that you should avoid relocating or even rotating the plant once buds form. N.C. Cooperative Extension also warns that continuous warm temperatures can cause buds to drop, so keep the plant away from heat vents and radiators.

How often should you water a Christmas cactus?

Water when the soil has dried out, then let the excess drain away completely. The University of Minnesota Extension recommends watering in a sink, removing any water left in saucers and decorative pots, and letting the soil dry between waterings. It names root rot from overly wet soil as one of the most common causes of death in these plants.

After the plant finishes blooming, water less often, then increase watering again in spring or early summer when new growth starts.

Soil and pot size matter too. The University of Minnesota Extension recommends a mix of 1 part sterile potting soil, 2 parts peat moss and 1 part sharp sand or perlite. Holiday cacti bloom best when kept somewhat pot-bound, and healthy plants may only need repotting every three years.

What does a Christmas cactus need after it blooms?

Bloom season can be long. N.C. Cooperative Extension says flowering can last 7 to 8 weeks if plants are kept at 68°F.

When the last flowers fade, the plant's year starts over.

Prune. Cut where two stem segments join. The University of Minnesota Extension says the plant will produce 1 to 2 new segments at each cut, which makes it fuller.

Feed in summer. Fertilize monthly from June through August with a balanced houseplant fertilizer at half strength.

Summer outdoors in part shade. The University of Minnesota Extension suggests a deck or patio with 3 to 6 hours of sun, ideally filtered light under a tree. Too much sun turns the branches pale.

Root the cuttings. Dip a cut piece in water and rooting hormone, plant it in damp builder's sand or a well-draining mix, and keep it bright and warm at 70 to 80°F. Check for roots after about 2 weeks.

FAQ

Is a Christmas cactus safe for cats and dogs?

Yes. The ASPCA lists Christmas cactus (Schlumbergera bridgesii) as non-toxic to both cats and dogs. For cut flowers, see this guide to flowers that are safe for cats.

Why is my Christmas cactus blooming at Thanksgiving?

It is probably a Thanksgiving cactus. Check for pointed teeth on the stem segments and yellow anthers. A true Christmas cactus can also bloom early if it gets cool, long nights early in fall, because N.C. Cooperative Extension notes that the earlier those conditions start, the sooner the plant flowers.

How long does a Christmas cactus live?

The University of Minnesota Extension says holiday cacti can live over 100 years.

Why does my Christmas cactus look limp when the soil is wet?

Too much water has likely damaged the roots. Let the plant dry out, make sure the pot and soil drain freely and keep it out of standing water.

Is a Christmas cactus a real cactus?

Yes. The University of Minnesota Extension describes holiday cacti as true cacti that are native to rainforests, which is why they need more moisture and less sun than desert cacti.

Can a Christmas cactus stay outside in summer?

Yes, in part shade. Bring it in before nights drop below 50°F, the limit N.C. Cooperative Extension gives.

Holiday Plants From Roots to Petals in Oakmont

Roots to Petals is an independent, woman-owned florist and plant studio at 527 Allegheny Avenue in Oakmont. The Plant Studio stocks hundreds of houseplants, from small ferns, succulents and air plants to large Ficus trees, and the shop's horticulturists help match each plant to a home's light and routine. If a plant you want is not in the studio, the shop says it is happy to order it, and potting is complimentary when you buy a plant and pot in the store, up to 8 inches. For more seasonal plants, read the guides to caring for an amaryllis, growing paperwhites indoors and houseplants that handle Pittsburgh homes and apartments.

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