Your Dieffenbachia’s leaves used to be a beautiful mix of deep green, creamy white, and electric yellow-green. Now they’re fading to a washed-out yellow or crisping up and turning brown. What’s happening to your Dumb Cane? And how can you fix it? We’ll review some of the most common causes for yellow and brown Dieffenbachia leaves, and suggest some possible solutions.
Dumb Cane foliage can become discolored in response to lots of different kinds of stress. Overwatering and underwatering are the most common issues. It’s also important to keep your Dieffenbachia out of harsh sunlight and extreme heat or cold, as all of these conditions are bad for its leaves.
There are a few other problems that can damage or dehydrate your Dumb Cane’s foliage – see our list below. Once you get your plant into more hospitable conditions, its health should improve, although the leaves that have already withered will stay that way. Here are some typical reasons why your Dumb Cane’s leaves may be turning yellow or brown:
#1: Normal Aging
Don’t be too quick to diagnose your Dieffenbachia with a problem, or you may wind up stressing it out by making unnecessary changes to its care. If the color change is limited to one or two of the lower leaves, there’s no cause for alarm.
Every leaf on a Dumb Cane eventually reaches the end of its life, at which point it turns yellow, shrivels up, and falls off. This happens with the lower leaves first, and it’s quite common for your Dieffenbachia to shed the foliage near the base of its trunk pretty quickly as it grows taller.
If that’s what’s happening here, you can breathe easy, though you should keep an eye on your plant in case the yellowing spreads further.
#2: Too Much Water
They say the difference between medicine and poison is dosage, and the same goes for watering houseplants. Your Dumb Cane needs water to live, but too much will kill it. If you water too frequently, causing the soil to stay wet for long periods, your Dieffenbachia’s leaves will start to lose their healthy color.
Why does this happen? First of all, roots need oxygen to operate, and they can’t get it when the potting mix is totally drenched. If your Dieffenbachia’s roots are sitting in wet soil for days at a time, the plant will start to notice the lack of oxygen, water, and nutrients. And your Dumb Cane could become infected with root rot, because waterlogged soil allows fungi and bacteria to multiply aggressively.
The symptoms of overwatering usually start with yellowing leaves. This discoloration typically begins with the lower leaves and rapidly spreads upward. In cases of chronic overwatering, any new leaves that grow in may be small and stunted.
When you see large-scale yellowing of your Dumb Cane’s leaves, check to see if the soil is damp. If it is, and it’s been more than a day or so since you last watered it, your plant is probably suffering from too much moisture.
Keep in mind that even if the soil appears fairly dry up top, it could still be soggy deeper down. Use a wooden chopstick or a soil moisture meter to test conditions in the bottom of the pot. If the soil is only slightly damp, that’s okay, but if it’s soaking wet, your Dieffenbachia is overwatered.
Fixing and Preventing Overwatering
If your Dumb Cane is only mildly overwatered, all you need to do is let the soil dry out before watering again. In the future, wait until the top two inches of soil are dry before watering your Dieffenbachia.
Root rot takes a lot more effort to fix. Warning signs include soft, squishy spots on the stem and leaves, as well as musty, swampy, or sour smells coming from the potting mix. If you notice any of the above, or if you think you’ve been chronically overwatering your Dumb Cane, take it out of the pot and check its roots right away.
Healthy Dieffenbachia roots are white and feel firm and springy to the touch. Infected ones will be gray, brown, or black, and their texture will be slimy and mushy. The only cure is amputation – snip away every root that shows even faint signs of infection. (Disinfect your snippers with 10% bleach or 70% isopropyl alcohol before each cut you make.) Then put your Dumb Cane in a sanitized pot with fresh potting mix.
Repotting in a new soil blend may be a good idea even if your Dieffenbachia doesn’t have root rot. Overwatering is often largely due to poor soil that retains too much moisture. Switching your Dumb Cane to a loose mix with good drainage can help you avoid swamping the plant in the future.
Our article on pots and soils for Dieffenbachia has some pointers on mixing up a healthy soil blend. We also offer a more detailed guide to rescuing a Dumb Cane from root rot here.
#3: Too Little Water
Good houseplant care is often about striking a balance between extremes. You don’t want to overwater your Dumb Cane, but you also don’t want to let it get too thirsty. If you do, its leaves will crisp up or turn yellow as their tissues die of dehydration.
Although underwatering and overwatering can both cause discolored leaves, underwatering often makes the foliage dry, crispy, and shriveled as well. Check the soil if you’re uncertain. Has it turned into a dry, solid cake and shrunk back from the sides of the pot? If so, you’ve been underwatering.
Not every case will be this obvious; if it’s unclear, test the pot with a moisture probe as we advised earlier. If it’s bone-dry, your Dieffenbachia needs water.
Fixing and Preventing Underwatering
The solution for a dehydrated Dumb Cane is easy: just give your plant a drink. Don’t be stingy, either. You want the potting mix to get fully saturated so that there’s extra water sluicing out the bottom of the pot. If it seems like everything you pour in runs out the bottom of the pot immediately, wait two hours and water it thoroughly again.
To avoid this issue in the future, start checking the soil in your Dumb Cane’s pot more often. Every 3-5 days is probably enough; Dieffenbachias are fairly drought-resistant. When the top two inches of the potting mix are dry and crumbly, it’s time to give your plant more to drink.
Dumb Canes are tough houseplants, and once yours is receiving enough water again, it should quickly return to its usual healthy self. The discolored leaves won’t turn green again, but they’ll soon be replaced by healthy ones. You can prune off the dead foliage if you want, but consider waiting a few weeks first, so that you’re not placing extra stress on your Dieffenbachia.
Dumb Canes are jungle plants that evolved to live in the partial shade provided by a rainforest canopy. Their thin leaves can’t handle the unfiltered light of the sun for long. Too much exposure causes them to release water vapor at an unsustainable rate, drying out and killing their cells.
This usually results in a bleached, faded appearance, with the foliage displaying large irregular patches of light brown or yellow discoloration. Unlike many issues that affect plant leaves, the scorch marks don’t tend to creep in from the tips and edges – they’ll start wherever the light is hitting your Dumb Cane the hardest and spread out from there.
That’s often a clue to the diagnosis. If you notice that the discoloration is clustered on the side of your Dieffenbachia’s body that faces the nearest window, it’s probably due to a sunburn.
Fixing and Preventing Sunburn
Once again, there’s nothing you can do about the damage that your Dumb Cane’s leaves have already sustained. All you can do is get the plant out of the sun to keep it from getting worse. You should also prune away any leaves that are completely fried, freeing up some energy that your Dieffenbachia can put into new growth.
As a rule, Dumb Canes should get no more than two hours of direct sun per day. If the light is falling right on your plant so that it casts a dark, sharp-edged shadow, that’s direct sun. Your Dieffenbachia prefers a location where the shapes of the shadows are clear, but their edges are slightly fuzzy. That indicates bright, indirect light.
East-facing windows are usually good spots for Dieffenbachias. If they let in any direct light, it will be in the morning, when the cool air gives your plant some resistance to sunburn. With a southern or western exposure, it’s best to hang some sheer curtains or move your Dumb Cane 4-6 feet back from the window. A north-facing window poses little risk of sun scorch but may be dimmer than your plant would like. Our post on Dumb Cane sunlight requirements has more detailed advice.
#5: Temperature Stress
Dieffenbachias are quite comfortable in the temperatures that are typical inside most modern homes: between 60 and 90 degrees. When they slip outside of that range, the resulting stress can cause their leaves to wilt and turn yellow.
If your Dumb Cane sits inside a hot, stuffy room during the summer, or beside a drafty window in the winter, its discolored leaves are probably due to temperature shock. Other possible sources of excessive heat and cold include air conditioning units, heating vents, fireplaces, and doors to the outside that could admit drafts.
Fixing and Preventing Temperature Issues
The only thing you can do for a Dumb Cane with temperature stress is to move it someplace more comfortable. With a little time in a healthier environment, it should recover. Some of the leaves and stems may die back in the meantime, but as long as the roots haven’t frozen, the dead portions should eventually be replaced by new growth.
A digital thermometer is a handy and inexpensive way to test whether a particular spot is safe for your Dieffenbachia. This one keeps a running tally of the temperature and humidity over time, giving you a sense of how they fluctuate throughout the year.
#6: Nutrient Shortage
Houseplants depend on their owners to supply the nutrients that wild plants get from rainwater, eroding rocks, and decaying organic material. If it’s been a while since you gave your Dieffenbachia any fertilizer, it could be suffering from a dietary problem. Shortages of nitrogen or phosphorus are especially likely to cause yellowing leaves.
You can often identify a nutrient problem because the leaves will be stunted or misshapen in addition to displaying unhealthy colors. Your Dumb Cane’s normally rapid growth may also slow down even if you’re providing lots of light and water.
Fixing and Preventing Nutrient Deficiency
When your Dumb Cane is malnourished enough that its foliage is dying, you should use a fast-acting fertilizer. That usually means a liquid fertilizer (or a powder that can be dissolved in the watering can), which makes the nutrients available to the roots right away.
A fertilizer with a 3:1:2 ratio of nitrogen, phosphorus, and potassium, like this one, provides the exact balance of nutrients in a healthy Dumb Cane’s body. However, that level of precision isn’t necessary if your plant’s pot and soil have good drainage and you’re watering properly. A 20:20:20 blend like this one is more cost-effective – it’s stronger, so you don’t need to use as much of the powder in each dose.
Start by giving your Dumb Cane a weak dose once a month, diluting it to ½ the strength recommended on the package (¼ if you’re using Jack’s Classic). You can step up the concentration little by little if your Dieffenbachia’s growth continues to lag.
#7: Mineral Buildup
Mineral ions can accumulate inside potting soil over time. When they reach high concentrations, they reduce your Dumb Cane’s ability to take up water and nutrients, causing the same discoloration you’d see in an underwatered plant. At extreme levels, these mineral salts can even draw moisture away from the roots.
This condition is commonly called fertilizer burn because synthetic fertilizer is the most common source of excess ions in houseplant soil, but it can also result from watering your plants with mineral-heavy tap water. The tips of your Dieffenbachia’s leaves will usually be affected first, turning brown and crispy before the rest of the leaf.
If you’ve ruled out issues with watering, sunburn, and extreme temperatures, and you’re sure that your Dumb Cane has all the fertilizer it needs, then mineral accumulation could be what’s messing with its leaves. You might get an additional clue in the form of crusty white salt deposits on the foliage.
Fixing and Preventing Mineral Accumulation
One way to resolve the problem of too much salt in the soil is to repot your Dieffenbachia in fresh, clean potting mix. However, being uprooted and replanted will place additional stress on the plant. If you don’t want to risk it, you can perform a soil flush, washing the extra minerals out of the pot by running a large volume of water through it.
Distilled water is best for this purpose. Use at least four or five times the total volume of your Dumb Cane’s pot, pouring it into the container slowly until the soil is thoroughly soaked and the extra water has all drained out the bottom.
Moving forward, you can repeat this procedure every month or two to keep the mineral salts from building up to unhealthy levels again. It’s also helpful to make sure that you saturate your Dumb Cane’s potting mix completely every time you water. The excess will flow out the base, creating a miniature soil flush with each watering – just be sure to empty the saucer afterward.
You should fertilize only during the growing season – if you give your Dumb Cane fertilizer when it’s not getting enough light to create new stems and leaves, it won’t be able to use the nutrients you’re providing. Instead, they’ll start to build up in the soil again. Taper off the dosage as you head into the fall and the days get noticeably shorter.
#8: Pest Infestation
There are several kinds of bugs that can feed on Dieffenbachia sap, draining away precious moisture and nutrients. Shriveled, yellowing leaves are one of the resulting symptoms. Check for the following common pests when your Dumb Cane’s leaves are unhealthy:
- Aphids. These insects have soft, round bodies – usually green, but sometimes brown, black, red, orange, or gray. Look for them on your Dieffenbachia’s youngest, softest shoots. You might also notice the sticky, sugary “honeydew” that aphids excrete.
- Mealybugs. Up close, these pests look like pill bugs coated in white fuzz; from further back, they look like little bits of dandruff. Like aphids, they produce honeydew, which you might discover before you spot the bugs themselves.
- Scale. Like mealybugs, but dark brown and rooted in a single spot. When you first see them, you might assume you’re looking at some sort of infection rather than a bug.
- Spider Mites. These tiny creatures usually have to be identified by the pattern of scarring they create on your Dumb Cane’s leaves – a random dusting of silvery-white dots. They also produce fuzzy, dirty-looking webbing on the leaves and stems of your plant.
Fixing and Preventing Pest Infestations
Dealing with Dumb Cane pests is a topic for an entire article – and what do you know, we wrote one! Here’s the simplified version:
Start by rinsing off the plant with a strong stream from a sink or garden hose, then wipe down every surface on your Dieffenbachia with a cotton swab soaked in rubbing alcohol (diluted to 20% strength). Next, shake up ⅓ teaspoon of gentle soap in 1 liter of warm water, mix in 1 teaspoon of neem oil, and spray this mixture over your Dumb Cane.
Plan on repeating this treatment every 3-5 days until the pests are wiped out. This will usually take several weeks. Keep your Dumb Cane away from any other houseplants in the meantime to prevent the infestation from spreading.
You can reduce the risk of pests entering your home by quarantining any new plants for at least a month after purchase. Keeping your Dieffenbachia in good overall health also makes it a less attractive target for bugs.
You’ll need to think through your entire care regimen to figure out why your Dumb Cane’s leaves are turning yellow or brown. On the bright side, this can serve as a learning experience that leaves your thumb greener than before. We hope the tips above help you restore the beauty and vigor of your Dieffenbachia’s leaves!