Calathea plants should be a focal point in any setting. It’s a stunning plant to admire up close, and from a distance.
The lush green foliage is a delight to any interior. When that’s spoiled by blotches of yellow spots, curling leaves on your Calathea, or worse, entire leaves yellowing, take it for the sign that it is that the plant is stressed.
Leaves Turning Yellow on Calathea Plants
Yellowing leaves are a sign of stress and there’s plenty of things that will stress out Calathea plants. Inadequate temperatures, low humidity, the wrong light conditions, fungal infections, insects, mineral accumulations in the soil. However, yellowing leaves can also just happen when the plant is acclimatizing to new growing conditions, such as a new location or if it’s just been repotted. Calathea don’t like change.
6 of the Most Common Stressors for Calathea
1.Watering Issues
A common cause of yellowing on any houseplants is caused by either over-watering or under-watering. The same is true of the Calathea, however, more important is the type of water you use.
Rainwater is purer than tap water so if you can harvest some rainwater, do that. If not, distilled, or at least leaving your water out for 24 hours for some of the chemicals to evaporate will do the world of good.
The problem with tap water is that it’s been treated to make it fit for human consumption. Salt and other minerals such as fluoride are added at water treatment plants.
Excess chemicals from treated water accumulate in the soil making it harder for the roots to absorb the water. When that happens, leaves start yellowing.
Water your Calathea with tepid water and until you see water pour out the drainage holes. An all-too-common watering mistake is to top it up, which will mean the soil isn’t being flushed of excess minerals.
2.Low Light Conditions
As with all plants, they grow best when their natural habitat is replicated. For the Calathea, that’s the jungle floor so the preferred lighting is dappled sunlight – bright and indirect.
Bright and direct light can cause the leaves to discolor.
Grown indoors, the best place for Calathea plants is up to 2-meters away from an east-facing window.
There, it will get a few hours of daily sunlight that isn’t as warm as a west-facing window therefore, there’s less risk of it overheating.
3.Temperature Swings
Calathea plants are finicky about the temperatures they grow in. Preferable is to maintain a consistent temperature that’s between 62ºF and 81ºF (16ºC to 27 °C).
When temperatures sway away from their preferred range, the plant will be stressed and it can cause the leaves to yellow.
When temperatures are too high, the leaves on Calathea plants start to curl before discoloring. Too low a temperature is worse as that will stunt growth.
4.Insufficient Humidity Levels
In their native environment, Calathea plants are used to humidity levels in the 90% range. Indoors, that’s near impossible to replicate.
They can tolerate humidity levels between 50% and 70%, but never lower than 50%. When the humidity drops under 50%, that’s when you’ll start to see the leaves on Calathea plants turn yellow.
A room humidifier is beneficial for growing tropical plants indoors, but if you struggle to maintain a relative humidity level of 50%, there are some things that can be done to increase local humidity around the plants.
Grouping
Grouping similar plants together is ideal because it creates a micro-growing climate. Humidity is increased through plant transpiration – the water that evaporates through plant leaves. The more plants you have, the more localized humidity rises.
For maximum effect, place a bowl of water in the middle of the collection of plants.
Humidity Trays
You can either buy a humidity tray to sit your plant pots on, or make one yourself by lining a tray with gravel or pebbles.
Pebbles and gravel hold water and release it slowly, helping to increase humidity. By resting your plant pots on top of a tray lined with pebbles, they benefit from increased humidity while being protected from the plant pot standing in sitting water.
Misting
Misting will slightly increase humidity but given the high humidity Calathea plants need, it won’t be practical. You’d be constantly misting the leaves daily, possibly multiple times each day.
Also, consider how you heat your home affects humidity. Heating systems produce dry air so if you’re noticing your Calathea plants leaves yellowing in the winter, it might be a good idea to move it to a room with higher humidity such as the kitchen or the bathroom.
The only thing to remember is that the leaves could still discolor due to having to acclimatize to new growing conditions.
5.Fertilizer Problems
As Calathea plants are grown indoors for their lush foliage, they don’t need a heavy feeding of fertilizer. The thing with fertilizers is that they change the soil pH.
Calathea plants prefer slightly acidic soil of 6.5. Too much can increase the pH and that’s the most likely reason for yellowing leaves. Too much fertilizer, rather than not using enough, or at all.
If you are feeding your plant with fertilizer, it’s beneficial to flush the soil every few months to prevent minerals from accumulating in the soil.
Too much mineral accumulation in the soil can lead to compaction, and that deprives the roots of oxygen.
The only time you really need to use a fertilizer with Calathea plants is if you’re watering with distilled water.
- Rainwater will have more beneficial nutrients.
- Tap water will have detrimental additives.
- Distilled water has nothing the plant can use.
If you using fertilizer, they do best with a liquid fertilizer applied every other watering or monthly during the growing season. Be careful not to overdo it though as too much fertilizer can cause the leaves of Calathea plants to turn yellow.
6.Spider Mites
Of all the usual indoor plant pests, spider mites are the most likely to infest Calathea plants.
Others are mealybugs, fungus gnats, aphids, and scale insects, but the spider mite is the most attracted to tropical plants and they love the Calathea.
The problem is they are only about 1mm in size and they live in colonies. By the time you see them, you’ll have an infestation on your hands.
They look like tiny white dots and you’ll see them on the underside of the leaves of your Calathea. The other thing you’ll notice is a fine webbing coating the leaves.
The yellowing on the leaves of Calathea is a result of mites sucking the sap out of the leaves. It’s the equivalent of drought because the insects steal the nutrients the plant needs to survive.
There a number of ways to kill spider mites, however, it needs to be done with care to avoid damaging the leaves. If you’re something strong like rubbing alcohol, it’s safer to dilute it.
Yellow Leaves on Calathea Plants FAQs
Will new leaves grow back on Calathea plants if I cut away the yellow leaves?
Before you prune a Calathea, take it out of the pot and inspect the roots and rhizomes. They should be white and firm. The rhizomes put out leaf shoots, however, only prune what you need to. Even if there’s only one leaf left, it’ll help with photosynthesis. Calathea leaves that have lost most of their color can be trimmed back to soil level, at which point the plant starts to focus its energy on new growth. Leaves will eventually grow back.
Should I be worried that the lower leaves on my Calathea are yellowing?
The lower leaves on Calathea plants are the first to yellow due to maturing. Simply prune them off to encourage new growth. The only time to be concerned about yellowing leaves is if it’s on new growth or some of the larger healthier leaves nearer the top. The bottom leaves are the first to yellow due to age, and those won’t recover.
Daniel has been a plant enthusiast for over 20 years. He owns hundreds of houseplants and prepares for the chili growing seasons yearly with great anticipation. His favorite plants are plant species in the Araceae family, such as Monstera, Philodendron, and Anthurium. He also loves gardening and is growing hot peppers, tomatoes, and many more vegetables.