Calathea leaves turn yellow when there is an environmental factor causing the plant stress. If the plant’s preferred growing conditions are not met, it will show its displeasure through a change in color. It is up to you to figure out what specifically is causing the discoloration so that you can fix it.
The most common causes of yellowing calathea leaves are aging, pests, drafts, overfeeding, transplant stress, temperature changes, insufficient or excess light, low humidity, underwatering and overwatering.
Why are the leaves on my calathea plant turning yellow?
Aging
Not all reasons for yellowing calathea leaves are sinister. It is completely normal for a calathea plant’s lower leaves to turn yellow and even brown as they grow older. This is because the plant wants to focus its resources on growing new leaves. It will choose to cut off the older leaves from resources so they die and fall off. You can help the leaf turnover by removing these old leaves while pruning the plant.
Since this is a normal part of the plant’s life cycle, there is nothing to fix and no need for you to worry. As long as the rest of the plant is vibrant and healthy and only the lower leaves are yellowing, you are doing a great job with your plant.
Repotting stress
Repotting a plant that has outgrown its pot is necessary, and can cause your plant to go through a considerable amount of stress. Give your plant enough time to get used to the change and it should be able to recover.
The good thing is that calathea plants are fine with being a bit rootbound, so you only really need to repot the plant every two years or so. The best way to know if your calathea needs repotting is if the plant needs to be watered more than twice a week now.
Disease
One of the most common diseases that can infect your calathea plant is the fusarium fungus. This disease causes your plant’s leaves to turn yellow and its stem to turn brown. You can use a copper fungicide to clear the disease up, but you can also just wash the old soil from the plant’s roots, throw away the soil, clean and sterilize the pot, and repot the plant using new soil.
Another disease, which is more serious than the fusarium, is the Cucumber Mosaic virus. It may not kill your plant but it does spread easily to other plants. It causes yellow streaks to appear on the leaves. Make sure you separate the infected plant from the other healthy plants as soon as possible. Dispose of the plant and the soil properly so the disease cannot spread, and make sure you wash and sterilize the pot before reusing it.
Pests
Calathea plants can get infested by scale insects, mealybugs and aphids, but the pests they are most prone to are spider mites. All of these insects feed on the plant and can cause stunted and yellowing foliage.
Spider mites are drawn towards calathea plants that are dry, so their presence can also be indicative of your plant being underwatered.
You can discourage spider mites from living on your calathea by misting the plant. You can also just remove the spider mites from the plant by spraying them with water once a week. Neem oil can also be used to kill these insects. Apply the oil on the leaves using a cotton ball once a week for a month to make sure all of the pests have been killed.
Drafts
If you keep your calathea plant inside the house and you cannot figure out what could possibly be turning its leaves yellow, you may need to check if there are drafts passing through the area where the plant is located. Maybe the plant is directly under an air conditioner, or maybe it is placed near a radiator. Having cold or hot air constantly blown toward it is not good for the plant and can cause its leaves to turn yellow due to stress.
Overfeeding
Calathea plants do not need to be fertilized often, which is why it is easy to make the mistake of overfeeding them. Too much fertilizer can cause the leaves to turn yellow, as well as a host of other issues.
You can still fertilize your calathea, but only do it once a month using a balanced fertilizer at half-strength.
You need to keep in mind that fertilizer is not a cure-all for ailing plants. Fertilizer is ideally used on plants that are healthy and actively growing. If you notice your calathea turning yellow after feeding, you have probably given it too much, so increase the dilution next time or simply reduce the frequency of feeding.
You can also keep the fertilizer from turning the plant yellow by flushing the soil with water to remove excess fertilizer that has built up in the soil. Flushing is done by letting clean water run through all of the soil for about two minutes until you can see the excess water flowing through the drainage holes at the bottom of the pot. Do this every few months, and it should count as watering, so do not water the soil again until after it has dried.
Temperature changes
Temperature extremes that are either lower than 62 degrees Fahrenheit or higher than 81 degrees Fahrenheit can both cause yellowing of calathea plant leaves. The changes in temperature stress the plant.
Calatheas can be tricky to keep happy during the winter, because even if you try to protect them from the cold using radiators or heaters, they do not do well near those heat sources either.
Transplant stress
Like most plants, calatheas also go through a period of stress when they are relocated to a new place. This is especially common for plants that are taken home from a nursery where the plant was grown in the most ideal conditions. It is difficult to replicate the conditions of a greenhouse in your home, so the plant has to adapt to new temperatures, humidities, light sources and watering schedules than those it has been used to.
There is nothing wrong with your plant; all you need to do is give it time to adjust to its new surroundings and it will recover soon enough. Make sure you provide it with conditions that are as close as possible to its natural habitat.
Insufficient or excess light
Both too much and not enough light can cause yellow leaves on your calathea. These plants require eight hours of indirect light everyday. The most ideal placement for the plant is next to an east-facing window, but you can still place it in a west or south-facing window as long as there is a curtain to somewhat diffuse the light. You can also just move the plant further away from the window so it does not get hit by light too much.
Low humidity
Calatheas are tropical plants, which means they like conditions with high humidity. This does not mean they will die in low humidity, but they will definitely be stressed, hence the yellowing leaves.
In the wild, calathea live in 90% humidity, but they can live in 50 to 70% humidity as houseplants.
You can help your plant by raising the humidity in your home with a humidifier. This is best for situations where you are growing multiple calathea plants, because it is an industrial solution for keeping humidity high. If you only have one or two calathea, there are easier ways to raise the humidity.
You can easily raise the humidity around your calathea by keeping it close to other tropical plants. Make sure there is still sufficient air flow between each plant. One of the downsides of this method is always making sure none of the plants gets infested with pests, because they will be able to spread quickly.
You can also increase the humidity for your calathea by placing trays with water near your plant, or placing the pot onto the tray but raising it using pebbles so that it does not touch the water. You can even use seashells to catch water so they can act as reservoirs.
One of the easiest ways to raise humidity is to mist the plant several times a day. Make sure the plant has good airflow around it because if it does not, and you keep misting it, fungal problems may arise.
Underwatering
The calathea plant can also become stressed if you allow its soil to become dry for long periods, leading to yellow leaves. The plant’s leaves do not always show when they are thirsty, so the more reliable way to tell if the plant needs watering is to check the soil. If the top few inches of soil are dry to the touch, you should water it.
Overwatering
Another common cause of yellowing calathea leaves is overwatering. Yes, the calathea is a tropical plant and it likes its soil moist, but you should never make the plant stand in soggy soil. If the plant is in soggy soil, the roots will drown and die. Dead roots are susceptible to root rot, which can travel up the roots and reach the stem and leaves, resulting in yellow leaves.
You can avoid overwatering by establishing a watering schedule suitable for the plant, using well-draining soil that does not retain water for too long, and using a pot that has drainage holes at the bottom so that excess water can easily drain out.
Conclusion
Calathea plant leaves turn yellow when there is an environmental factor causing stress to the plant. You need to be able to identify what this stressor is so that you can fix the problem as soon as possible.
The most common causes of yellowing calathea leaves are aging, pests, drafts, overfeeding, transplant stress, temperature changes, insufficient or excess light, low humidity, underwatering and overwatering.
Image: istockphoto.com / Elena Grishina