Christmas cactus

The Christmas cactus is not a desert plant. Its ancestors grow in the coastal mountains of south east Brazil, perched in the forks of trees and in pockets of leaf litter on rock, in shade and humidity, and the flat jointed stems that look like leaves are how it makes the most of dim light. Almost every mistake made with this plant comes from treating it as though it came from a desert. It wants bright indirect light, a bark based mix, regular water in the growing season, and one particular sequence of darkness and cool to make it flower.

Light

Bright indirect light all year. An east window is close to ideal. Direct sun through glass bleaches the segments to a dull purplish red and burns pale patches into them, which never green up again.

Water

Water when the top 2 to 3 cm of the mix is dry, roughly every eight days in the growing season and every fortnight in winter. It should never be left bone dry for weeks the way a desert cactus can be, and it should never sit in wet compost either. A free draining bark based mix makes both easier to get right.

Making it flower

This is the whole art of the plant, and it is entirely mechanical. Schlumbergera sets buds in response to long nights and cool temperatures, not to a date. About six weeks before you want flowers, give it twelve to fourteen hours of complete darkness every night, keep it around 15 degrees, water sparingly and stop feeding. A spare room with the curtains drawn, or a cupboard it goes into each evening, both work, and a street lamp or a hallway light through a doorway is enough to prevent the whole thing.

Once buds appear, stop managing it and leave it alone. Bud drop is the single most common complaint about this plant and it is caused by change: a move to another room, a swing in temperature, a draught from a door, an irregular watering. Choose the final position before the buds set.

When it flowers south of the equator

The name is a northern hemisphere accident. Because the plant responds to shortening days, a Christmas cactus in Australia, New Zealand or South Africa flowers in the southern winter, around May to July, and the six weeks of long nights fall in autumn rather than in spring. Nothing about the method changes, only the calendar. A plant moved between hemispheres takes a season to reset.

Feeding and repotting

Feed at half strength monthly from after flowering until late summer, then stop, because the drop in feeding is part of the signal that autumn has arrived.

Repot in late winter once the flowers are over, and only when the roots have genuinely filled the pot, because it flowers better slightly crowded. Every third year is plenty.

Pruning and propagation

After flowering, twisting a couple of segments off the end of each stem makes the plant branch and flower more heavily the following year. Everything you remove is a cutting.

Take a piece of two or three segments, twist rather than cut it so the joint separates cleanly, leave it on a dry surface for a day so the break seals, then push the bottom segment into damp gritty mix. Keep it barely moist and out of direct sun and it roots in three to four weeks. Several cuttings around the edge of one pot make a full plant quickly.

Ailments

No flowers means the dark treatment was missed or interrupted. Falling buds mean something changed after they formed. Shrivelled segments need a finger in the compost before you decide whether the cause is drought or rot. Bleached patches are sunburn. The ledger below has the rest.