Calathea plants, Calathea sp., are a popular tropical species that make extremely great houseplants due to their low light requirements, limited water usage, and vibrant broad foliage.
Known for their abundance of green leaves and often striking purple undersides, Calathea plants are a true delight to have around, which is why yellowing leaves are such an awful sight.
In this article, you will find a list of the top 5 reasons why your Calathea leaves are turning yellow and what to do to fix them.
Why Do Calathea Leaves Turn Yellow
The unfortunate event of leaf yellowing is called chlorosis and occurs when environmental factors disrupt the plant’s ability to create chlorophyll.
When chlorophyll production is prevented or disrupted, photosynthesis is unable to take place and as a result, leaves lose their green color.
Causes of Calathea Leaves Turning Yellow
The most common reasons for the yellowing of Calathea leaves are issues with watering, soil nutrient problems, temperature fluctuations, low humidity levels, pests, and diseases.
Each reason presents with differing symptoms and unsurprisingly has different needs when it comes to fixing and presenting.
Here’s a look at what I mean by that in closer detail.
Watering Issues
Issues with watering schedules and soil moisture levels are the most common reasons why Calathea plant leaves turn yellow.
To fix issues soil either remains saturated or becomes dry too quickly and is unable to retain enough moisture, you will need to transplant your Calathea into a soil mixture that retains moisture but is still well-draining. My go-to soil mix is as follows:
- 1 part Coco Coir
- 1 Part Perlite
- 1 part Vermiculite
- 1 Part Worm Castings
Overwatering
Yellow wilting leaves, stem rot, and severely stunted growth are symptoms of overwatering.
When overwatering occurs, empty the catch tray and stop watering until the top 2 inches of the soil has dried out. Feed a supplemental liquid fertilizer to help it recover.
Under-watering
Yellow leaves, wilting, and crisping of edges are common symptoms of under-watering. If left to dry out completely, you can expect eventual root decay and nutrient deficiencies.
If under-watering has occurred, soak the container until the water runs freely through the drainage holes at the bottom of the container. Repeat several times until the leaves of your Calathea start to perk up. This should happen within an hour or so.
Using Unfiltered Tap Water
Yellow spots and leaf curling on your Calathea are signs of damage from using unfiltered tap water.
The water from our taps will often contain chlorine and/or fluoride which quickly builds up in the soil and is especially common in potted or container plants. In addition to the changes that affect leaves, root growth can also be inhibited, nutrient deficiencies can occur, and your plant can go into shock.
Promptly flush your Calathea with filtered water or rainwater until it thoroughly drains and avoid using unfiltered water thereafter. Replanting in fresh soil may also be necessary if these compounds have been allowed to build up.
How To Water a Calathea
Only water if the top 2 inches of the soil are dry. Depending on the temperature and humidity in your region, on average this will be once per week in the growing season and as little as once per month during the dormancy of winter.
Use filtered water or rainwater rather than tap water thereafter.
Soil Nutrient Issues
Yellowing of leaves is often caused by a lack of nutrients due to nutrient-poor soil or leaching, the inability of plants to uptake available nutrients or an excess of nutrients in the soil.
Nitrogen
Yellowing of the entire leaf surface starting with the older leaves first is a sign of nitrogen deficiency in Calathea plants.
To fix a nutrient deficiency, apply a 1-inch thick top dress that contains 50% worm castings and 50% organic potting soil mix, and water thoroughly.
Iron
Yellowing of the entire leaf except for the veins is a sign of iron deficiency.
Where soil pH levels are too high, the plant will be inhibited from absorbing the iron that would otherwise be available from the soil.
According to the University of Arizona, there are 3 effective methods of correcting iron deficiencies. Acidify soil (where soil pH is too high, or apply a chelated iron fertilizer either to the soil or directly to the foliage.
Magnesium
Yellowing of the veins of Calathea leaves is a clear indication of magnesium deficiency. This is especially common in plants that have been over-fertilized with a potassium-rich feed as the plant will absorb potassium over magnesium.
When this occurs, flush the soil out with water thoroughly and use a supplemental liquid fertilizer that contains additional magnesium.
Avoid using Epsom salts unless magnesium is severely depleted, as studies have found that the automatic application of Epson salt can injure plant roots and contaminate the soil.
Over-Fertilizing
When plants absorb excessive amounts of fertilizer, they begin to show signs of yellow leaves with curled edges. This is caused as a result of high soluble salt toxicity.
The best way to get rid of salt buildup in the soil is to flush the soil with enough fresh water to fill the container. This should be repeated 2 – 3 times over a few weeks, allowing time in between for the soil to dry out.
Avoid fertilizing for at least a month.
How To Fertilize a Calathea
I recommend using a liquid fertilizer that can be diluted with water when feeding Calathea. The leaching that occurs when using liquid feeds will help to prevent a salt build-up in the soil and will prevent your plant from absorbing excessive amounts of fertilizer.
When using liquid feeds, apply from March through to October. A monthly feed will be sufficient.
If you prefer to use slow-release granules, I recommend feeding no more than 2-3 times during the active growing season. Over-application of granules may lead to a salt build-up.
Select a fertilizer with a relatively low N-P-K ratio such as 5-5-5 or 10-10-10. Avoid feeds with a high percentage ratio of phosphorous and potassium as this may prevent your plant from absorbing other key nutrients.
Never feed while your plant is dormant (November through to the end of February). Your plant will not be growing much (if at all during this time) and simply will not be absorbing nutrients.
Temperature Fluctuations or Excessive Sunlight Exposure
Yellowing dead spots, wilting, and crisping of Calathea leaves is indicative of rapid or frequent temperature fluctuations, or excessive sun exposure. These symptoms can be particularly common after propagating when plants tend to get moved around as well as if you change its location.
Calathea plants are tropical understory species that prefer bright yet indirect sunlight, and temperatures between 65 – 85 degrees Fahrenheit.
Relocate where the Calathea will receive 8 – 10 hours of filtered sunlight per day, and move it at least 9 feet away from main doors, north windows, or heat sources.
Low Humidity
Yellowing leaves with browning edges can indicate too low humidity.
Calathea needs to be located in a spot with at least 50% relative humidity. Consider placing it in a sunny bathroom where the shower is used regularly, or in a warm kitchen. Alternatively, invest in a humidifier or place your plant next to other tropical.
Pests and Disease
Household pests, like spider mites, and bacterial infections, like leaf spot disease are both common reasons for Calathea leaves to turn yellow.
Spider mites
Tiny yellow dots, webbing on the underside of leaves, and stunted growth are all signs of spider mite infestations.
If you suspect a spider mite infestation on your Calathea plant, then isolate it, wash all affected areas to remove as much of the infestation as possible, and treat with an application of all-natural essential oil sprays that contain neem, lemongrass, and lavender.
Leaf Spot Disease
Yellowing, water-soaked spots that turn black are an indication that your Calathea is infected with bacterial leaf spot disease. This is caused by Pseudomonas leaf spot
This common disease is very difficult to control and treat, and your best option may be to destroy the affected plant.
Avoid overhead watering as a preventative measure and check your plant regularly for early signs and symptoms. When symptoms are mild, treat with applications of a copper-based bactericide.
Citations
- University of Arizona – Methods of correcting iron deficiencies
- Washington State University Master Gardener – Epsom Salts
- University of Florida, IFAS – Bacterial Leaf Spot and Blight of Calatheas
Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.
