Why Do Christmas Cactus Turn Yellow?

One of the great things about the Christmas cactus (Schlumbergera x buckleyi) is that it blooms around Christmas. Have trouble blooming? Read Why Isn’t my Christmas Cactus Blooming?

Of course, that doesn’t mean this plant with Brazilian roots isn’t attractive the rest of the year.

Its flat, jointed stems have more rounded edges than its cousin, the Thanksgiving cactus (Schlumbergera truncata), which has saw-toothed ones. Strictly speaking, neither plant has true leaves. Photosynthesis happens in the green stem segments. Most of us call them leaves anyway, so I will too.

So what do you do when those green stems turn yellow? Don’t panic. Yellow is a message, and you can decode it. Here are the five things to check.

Why Is My Christmas Cactus Turning Yellow?

There are five common reasons, listed here roughly from the most minor concern to the most serious. One thing to know up front: Clemson’s houseplant disease guide says that when a houseplant turns yellow, overwatering is most often the cause. So if you only have a minute, check the soil and the drainage first.

Poor Light Conditions

In the wild, Schlumbergera cacti grow on tree branches in shady rain forests, so bright sun is not its natural habitat. Bright sun in summer can make holiday cacti look pale and yellow, though full sunlight is beneficial during fall and winter. The Missouri Botanical Garden says container plants moved outdoors into full sun during the growing season end up with bleached foliage. University of Minnesota Extension adds that excessive sunlight may cause pale green branches and sunburn.

What does the plant want? UF/IFAS Gardening Solutions says bright, indirect light, within six feet of a south-, east- or west-facing window.

Too little light can also be a problem. Too little light is also among the reasons houseplant foliage turns yellow, so a dim corner isn’t a safe hiding place either.

To check, look at your plant at different points in the day. If it’s dim, move it closer to a bright window. If summer sun is hitting it directly, pull it back from the glass or add a sheer curtain.

Seeing purple instead of yellow? More on Christmas Cactus leaves turning purple.

Not Enough Water or Improper Watering

Watering by the calendar is a classic mistake. Water when the plant needs it, which means when the upper inch of soil feels dry. The Chicago Botanic Garden gives the same top-inch test. So push a finger in about an inch. Dry? Water. Still damp? Wait.

Don’t overcorrect, though. Avoid letting the plants get too dry between waterings: lower houseplant foliage may turn yellow when the soil stays too dry for an extended time.

When you do water, soak the soil until water runs out of the drainage holes, wait a few minutes, then empty the saucer. Never let water stand in the saucer. A good soak has a bonus: drenching houseplants now and then leaches salts out of the potting soil.

Water quality can matter too. Some houseplants are sensitive to fluoride or chlorine in tap water, so try letting the water stand at room temperature for 24 hours before using it. That is general houseplant advice, not specific to Christmas cactus.

Humidity helps as well. Christmas cactus prefers humid conditions, and homes are often dry. The trick is a pebble tray: set the pot on a small container of pebbles, then pour water over the pebbles without letting the water rise above the bottom of the top layer of pebbles.

Malnutrition

In nature, Schlumbergera cacti live on tree branches. In a pot, yours depends on you for food. Too little fertilizer is among the causes of yellow houseplant foliage, and holiday cacti need more magnesium than many plants.

Feed during the growing season with a soluble fertilizer at half strength. Recommended schedules differ a little: monthly from the start of new growth in late winter or early spring through summer, stopping in late summer; monthly from June through August; or every one to two months from April to September. Whichever you choose, follow the fertilizer label, and see our guide to the best fertilizer for Christmas cactus.

Fresh soil matters too. A healthy holiday cactus needs repotting only about every three years, and spring is best. Use a well-drained, airy mix. One option is 60 to 80 percent potting soil with 20 to 40 percent perlite; another is one part potting soil, two parts peat moss and one part sharp sand or perlite. And skip the giant pot: Christmas cactus prefers to be a bit root-bound.

Infestations and Disease

Christmas cactus can host several common houseplant pests. The list includes mealybugs, soft brown scale, red spider mites, aphids, fungus gnats, thrips and whiteflies.

These pests feed on the plant’s sap, and it shows. Aphids cause yellowing and misshapen growth, spider mites can leave leaves bronzed or yellowed, and whiteflies can make leaves turn yellow.

Look for sticky, shiny leaves. Many sap-sucking insects excrete a sugary waste called honeydew, and sooty mold fungi may grow on it. University of Maryland Extension says sooty mold does not infect plants, though heavy growth can shade the leaves and stress the plant. Sticky or sooty leaves are a clue to go looking for pests.

Fungus gnats have a soil connection. Their larvae feed on decaying organic material or fungi in the soil, and some feed on roots. The problem is worst when overwatering occurs, and dry conditions kill the larvae, so letting the soil dry between waterings helps.

Act quickly, and start gently. Isolate the plant from your others, wipe aphids and mealybugs off with a cotton swab dipped in rubbing alcohol, and scrape scale off with a fingernail. Insecticidal soap can eliminate an early infestation, but it works only on contact, and hidden pests or eggs often mean more than one treatment.

What about neem oil? The National Pesticide Information Center says neem oil and some of its purified components are used in over 100 pesticide products, and that azadirachtin, its most active component, reduces insect feeding and acts as a repellent. Always follow the label. Only a few pesticides are labeled for indoor use on houseplants, so check that the label allows it, or treat the plant outdoors and bring it back in once it has dried completely. Use the product’s own directions for how often to apply.

Too Much Water

This is the big one. Yellowing is most often a symptom of overwatering, and root rot, the loss of roots from overly wet soil, is one of the most common causes of death in holiday cacti. Root rot is the major disease of Christmas cactus, and it can be prevented by avoiding excessive watering.

Read: How Often To Water Christmas Cactus

Christmas cactus tolerates dry, slightly under-watered conditions, but its soil should not be allowed to dry out or become overly moist, and root rot may occur if the soil is kept overly moist.

The mix and the pot matter as much as your watering can. The potting medium must be well drained with good aeration, because these epiphytic cacti don’t grow well in heavy, wet mixes, and the soil should never become waterlogged, especially during the dark days of winter. Containers need enough holes for water to drain easily. Common culprits are a heavy mix, too few drainage holes and a saucer full of water.

How do you spot root rot? A plant that looks wilted even though the soil is wet may be suffering from too much water. With fungal root and stem rot, the foliage turns gray-green and the plant wilts, stems rot at the soil line, and the roots are dark and mushy. Black, wet, slimy lesions that start at the soil line and climb the branches are bacterial soft rot; destroy infected plants.

What should you do? Let the plant dry out, and make sure the pot drains freely and the plant isn’t sitting in water. Then slide the plant out and look at the roots. If only a few roots are infected, you can cut them out and repot in sterile soil. If most of the roots are dark, soft and dead, it is better to discard the plant.

If the rot is too severe, don’t write off the whole plant just yet. Holiday cacti are easy to propagate from cuttings taken in May or June, so healthy stem segments can start a new plant.