The Calathea family of plants is delicate, demanding, and delightful, but it isn’t without its challenges. White spots marring the lovely foliage of my captivating Calatheas are among the dramas I’ve had to deal with. But, even though it’s a common issue, it has a simple solution.
In good health, the sap from a healthy, well-tended Calathea plant can leave white marks on the leaves as they dry. Fungal infections, pest damage, or nitrogen deficiency can also be blamed. White spots can also be caused by sunburn or edema.
The size, texture, and location of white spots can help determine what’s going on, so it’s essential to take a closer look. White spots on Calatheas can be caused by a variety of things.
White Crystals on Calathea Leaves
Does your Calathea have white spots that feel sticky or salty to the touch? Do they wash off easily with water, only to reappear on a different part of the leaf the following day?
If this is the case, then the spots result from a process known as guttation.
In the humid climate of a tropical region like yours, plants like Calathea are accustomed to a high humidity level. Calatheas struggle to maintain mineral balance in their leaves and stems in their rainforest habitat.
Calatheas produce mineral-rich sap from particular pores known as hydathodes to maintain that balance. These pores expel excess salts and sugars in an undetectable trickle until equilibrium is restored. When dried, this sap leaves white marks.
Solution
Guttation occurs when the Calathea is well watered and well-nourished and when there is a high humidity level around the plant. The white marks on the leaves of your Calathea are a good sign that it is doing well.
To restore the leaves to their original, pristine state, all you need to do is wipe them down with a damp cloth.
Pest Infestation
Mealybugs
Mealybugs are likely to be found in clusters around the plant’s veins, which are soft and fluffy. These creepy crawlers weaken the plant by feeding on Calathea’s sweet sap.
Mealybugs may be to blame if the spots on your Calathea are mainly on the underside of the leaves, and they leave behind a sticky residue.
Spider Mite
They also suck the sap from the leaves, nearly undetectable to the naked eye. Then, as they spread across the leaves, they prefer to hide in the tiniest of spaces.
There are mites if your white patches are tiny and change color from white to brown. In addition, be on the lookout for fine filaments.
They are known as “spiders” for a good reason, as they leave a trail of webs behind them when they crawl. However, the mite is more straightforward to spot than the web in many cases.
White Scale
Insects with a shield-shaped outer shell are called white scale. To get their hands on the sweet Calathea sap, they puncture its veins.
A wart-like bump appears on the leaf’s structural parts. Take a closer look by scraping one off with a fingernail, and you’ll find a tiny insect and a lot of sticky sap inside.
Thrips
Unlike the other three tiny terrorists on this list, Thrips prefer to eat the leaves of the Calathea. This is because the cells themselves have scraped away, resulting in patches of translucency that vary in size and shape.
I always think of the thrips as tiny dark dots that remind me of iron filings or the shavings from an electric shaver.
How to Get Rid of Insects on Calathea
Spray the infested Calathea with a garden hose or showerhead. Pests will be blasted off the plant by the force of the water. Before reinstalling the Calathea, allow the leaves to dry thoroughly.
You can also use rubbing alcohol-soaked cotton tips to get rid of them. Thanks to this method, your plant will be free of pests, which remove the insect from the plant and dries out its body so it cannot re-infest it.
I’d recommend neem oil for severe infestations. Dilute properly and repeat the treatment once a week to kill any eggs hatched since the last treatment. (Check out the prices on Amazon here)
When pests are discovered in one piece of your collection, be sure to check the rest. They spread quickly, just like bad news. You may have to deal with more than just the Calathea, which is obviously sick.
Fungal Diseases
Poor ventilation and a soggy growing medium are common causes of fungal diseases, even if their symptoms and treatments vary.
Suppose a specimen can resist a fungal spore in good conditions. In that case, it will become infected if the growing conditions are poor.
Besides the solutions below, if you find fungal disease on any plant in your collection, that means you need to improve the airflow in your home.
Your growing medium should be checked to ensure that it drains well and isn’t too wet. This will also protect your Calathea from root rot, preventing spotting of the leaves.
Powdery Mildew
Powdery mildew is caused by the Oidium family of fungi. It appears as soft, silvery patches on the leaves of the affected plants. The leaf beneath eventually dies and turns brown and papery.
If you run a finger over the white spot and leave a silvery residue on your hands, mildew is most likely the culprit.
Solution
Remove the diseased leaves from your Calathea and discard them in the garbage.
For larger mold infestations, milk spray is an effective remedy. Spray the affected Calathea leaves liberally with a solution made from two teaspoons of milk diluted in one quart of warm water.
Spray the undersides and the tops of the leaves, and don’t forget about the healthy-looking ones either. If your Calathea is a highly variegated cultivar, mildew can be difficult to spot in its early stages.
White Mold (Saprophytic fungus)
This harmless fungus lives in the growing medium, breaking down organic matter and releasing the nutrients inside back into the mix. Then, over-vigorous watering splashes on Calathea itself and gets it to the leaves and stem.
There is a good chance that the white marks are powdery, like talc, with no flakiness or damage to the leaf underneath. However, fluffy white specks may also appear on the surface of your growing medium.
Solution
To remove white mold from your Calathea, wash the leaves and stems.
Next, clean the growing medium to remove any mold that has grown on top of it. The first inch or two may require replacement. Adding a few tablespoons of cinnamon on top will stop it from growing back.
Gray mold (Botrytis)
Though it is more commonly associated with rotting strawberries, botrytis will happily nibble away at the delicate parts of Calatheas as well.
It’s a sign of botrytis if your young leaves develop long lesions covered in gray fuzzy patches with an almost velvety surface.
Solution
Botrytis should not be taken lightly. Remove any diseased leaves and toss them in the garbage as soon as possible. Use a robust copper-based fungicide and always follow the manufacturer’s instructions when applying the treatment. (Check out the prices on Amazon here)
Nitrogen Deficiency Cause White Patches on Leaves
Your Calathea, like all plants, needs a consistent supply of nitrogen to produce strong, healthy leaves. In the absence of adequate fertilization, the leaves become weak and brittle. Often, they are left with patches of white.
Treating nitrogen deficiency if the Calathea has a weak overall condition and the white areas on the leaves appear faded or washed out.
You can use an all-purpose liquid fertilizer to supplement your watering schedule. But, when it comes to Calatheas, it pays to be frugal.
Those pale feeble leaves shouldn’t take long to perk up and start showing their charismatic best because they don’t require much.
Sunburn Cause the Leaves to Appear White
In the shadows of the rainforest floor, Calatheas are perfectly adapted, and direct sunlight burns their delicate foliage.
The pigments in the leaves are annihilated by powerful ultraviolet radiation from the sun. This causes the leaf to appear white at first, but the color fades and becomes dry and brown as it ages.
You may have sunburned your Calathea if your white spots are wide and mostly appear on the leaves facing your light source.
Relocate the Calathea to a less sun-drenched area of your growing space. Bright, indirect light is all that’s needed for these dazzling beauties.
I usually leave sun-damaged leaves in place. As long as they have at least half of their color, the leaf gives your Calathea food. But if you can’t bear to look at them, you can remove them from the plant without harming it.
Edema Makes the Leaf Appear Blistered
A humid and wet environment is a natural habitat for Calathea. Guttation is a natural response to excess moisture in healthy plants. Still, edema can occur if a plant is overworked or poorly supported.
Excess water accumulates in the leaves and stems of the plant. As a result, affected tissue may appear blistered, then dry out, leaving pale, flaky areas. To the touch, the stems and stalks become corky or springy.
Solution
To begin with, stop watering! In over-watered plants, edema is a common side effect, especially if the growing medium is not free-draining.
Make sure you don’t get this one wrong because Calatheas are notoriously picky about their watering schedules!
Depending on the plant’s age, pot size, and season, I prefer to use a meter to check the root moisture level.
Re-potting may be necessary if water levels are constantly fluctuating. Peat moss and perlite should be added to a standard organic mix.
The moss keeps the Calatheas’ delicate moisture level in check, while the perlite provides the necessary drainage.