How to make a Christmas cactus bloom again

A Christmas cactus can outlive its owner. The University of Minnesota Extension notes that these plants can live more than 100 years and are often passed down through families.¹ What frustrates people is the year it refuses to flower. The fix is rarely fertilizer or a new pot: it is light and temperature.

Not a desert cactus

Holiday cacti are true cacti, but they come from rainforests, where they grow on tree branches in the shade.¹² That is why they want bright but filtered light, relatively moist soil for much of the year, and high humidity, unlike the cacti and succulents of dry deserts.¹

There are three common types. The Thanksgiving cactus and the Christmas cactus flower in late fall and winter, and the Easter cactus in late winter or spring. The names only roughly describe when they bloom.¹

What triggers the flowers

Holiday cacti are "short-day" plants: they form flower buds as the days get shorter in fall. Cool nights are the other half of the signal.¹ The University of Minnesota gives clear numbers:¹

• With night temperatures around 55°F, plants bloom in about 5 to 6 weeks, sometimes regardless of day length.
• With nights of 60 to 65°F, they need at least 12 hours of complete darkness every night for about 6 weeks.
• Above 65°F at night, they are unlikely to bloom at all.

Clemson Extension asks for even longer nights, 14 hours or more of continuous darkness for at least 6 weeks starting around mid-September, and warns that as little as 2 hours of interrupted light can stop buds from forming.² In practice, that means a cool room that nobody lights up at night: a spare bedroom, or a porch until frost threatens.

A simple fall routine

The University of Minnesota suggests leaving plants outdoors in a protected spot until just before frost danger, so shorter days and cooler nights do the work.¹ Indoors, choose a cool, bright spot with days of 65 to 70°F and nights of 55 to 65°F.¹ Buds normally appear in 3 to 4 weeks, and once they are set, day length no longer matters.²

Why buds fall off

Dropped buds are the most common complaint. Too much water can cause flower buds to drop, along with wilting and root rot.¹ Continuous warm temperatures can do it too.² So keep the plant cool, water it only once the soil has dried, and do not let it sit in water in a saucer.¹

Year-round care

• Soil and pot: use a well-drained mix in a pot with drainage holes. Holiday cacti bloom best when slightly pot-bound, and healthy plants may only need repotting every three years.¹
• Water: let the soil dry out between waterings, and drain the pot in the sink.¹
• Feeding: fertilize monthly from June through August with a balanced houseplant fertilizer at half strength.¹
• Summer: a spot outdoors in part shade suits them; too much sun can turn the stems pale.¹

Thanksgiving or Christmas cactus?

Many plants sold as Christmas cacti are actually Thanksgiving cacti, which bloom about a month earlier. Clemson's tip: look at the flat stem segments. The Thanksgiving cactus has 2 to 4 pointed, saw-toothed projections along each edge, while the Christmas cactus has rounded edges.² Its pollen-bearing anthers are yellow, while those of the Christmas cactus are purplish-brown.²