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. Clemson Cooperative Extension says 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, according to Clemson’s Christmas cactus factsheet, so bright sun is not its natural habitat. That factsheet says bright sun in summer can make holiday cacti look pale and yellow, though it also says 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. Clemson lists too little light 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. UF/IFAS says to water only when the upper inch of soil feels dry, and 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. UF/IFAS also says to avoid letting the plants get too dry between waterings, and Clemson says 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, as the Chicago Botanic Garden describes. Clemson says never to let water stand in the saucer. A good soak has a bonus: Clemson suggests drenching houseplants now and then to leach salts out of the potting soil.

Water quality can matter too. Clemson says some houseplants are sensitive to fluoride or chlorine in tap water, and suggests 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. The Chicago Botanic Garden says Christmas cactus prefers humid conditions, and homes are often dry. Its 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. Clemson lists too little fertilizer among the causes of yellow houseplant foliage, and says holiday cacti need more magnesium than many plants.

Feed during the growing season with a soluble fertilizer at half strength, as Clemson and University of Minnesota Extension suggest. The schedules differ a little. Clemson says monthly from the start of new growth in late winter or early spring through summer, then stop in late summer.

University of Minnesota Extension says monthly from June through August. UF/IFAS says 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. Clemson and University of Minnesota Extension both say a healthy holiday cactus needs repotting only about every three years, and Clemson says spring is best. Use a well-drained, airy mix. Clemson suggests 60 to 80 percent potting soil with 20 to 40 percent perlite.

University of Minnesota Extension and the Missouri Botanical Garden suggest one part potting soil, two parts peat moss and one part sharp sand or perlite. And skip the giant pot: UF/IFAS says Christmas cactus prefers to be a bit root-bound.

Infestations and Disease

Christmas cactus can host several common houseplant pests. The Missouri Botanical Garden lists mealybugs, soft brown scale, red spider mites and aphids. Clemson adds fungus gnats, and its houseplant pest guide also covers thrips and whiteflies.

These pests feed on the plant’s sap, and it shows. Clemson says 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 Clemson says 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. Clemson says their larvae feed on decaying organic material or fungi in the soil, and some feed on roots. It says the problem is worst when overwatering occurs, and that dry conditions kill the larvae, so letting the soil dry between waterings helps.

Act quickly, and start gently. Clemson advises isolating the plant from the others, wiping aphids and mealybugs off with a cotton swab dipped in rubbing alcohol, and scraping 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 (NPIC) 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. NPIC also says to always follow the label.

Clemson adds that 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. Clemson’s disease guide says yellowing is most often a symptom of overwatering, and University of Minnesota Extension says root rot, the loss of roots from overly wet soil, is one of the most common causes of death in holiday cacti.

Clemson’s Christmas cactus factsheet calls root rot the major disease and says you can prevent it by avoiding excessive watering.

Read: How Often To Water Christmas Cactus

The Missouri Botanical Garden says 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 stays too wet.

The mix and the pot matter as much as your watering can. Clemson says the potting medium must be well drained with good aeration, because these epiphytic cacti don’t grow well in heavy, wet mixes, and it says not to let the soil become waterlogged, especially during the dark days of winter.

University of Minnesota Extension says 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? University of Minnesota Extension says a plant that looks wilted even though the soil is wet may be suffering from too much water. With fungal root and stem rot, it says the foliage turns gray-green and the plant wilts, stems rot at the soil line, and the roots are dark and mushy.

It also describes black, wet, slimy lesions that start at the soil line and climb the branches as bacterial soft rot, and says to 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, as University of Minnesota Extension advises. Then slide the plant out and look at the roots.

Clemson says that 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, Clemson says it is better to discard the plant.

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