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Brown Spots on Calathea Leaves (Causes and Treatment)

Calathea leaves have stunning patterns and colors making them a highly attractive foliage plant.

With such gorgeous leaves, one problem that can definitely affect its beauty is the appearance of brown spots.

Brown Spots on Calathea Leaves can be a result of diseases like algal leaf spot, anthracnose, septoria leaf spot. Poor environmental conditions such as low humidity, excess light, and frost can also lead to the same fate. In rare cases, pest infestation is the culprit behind the brown spots.

In this article, I will talk about this particular problem and give you pointers on how to deal with it. 

Brown Spots on Calathea Leaves
Brown Spots on Calathea Leaves

Causes of Brown Spots on Calathea Leaves 

Following is the discussion on each of the possible causes of brown spots. For the most part, the symptoms may appear the same.

That is why you have to be keen on observing your calathea plants to know which exactly is the cause of the brown spots.

Algal Leaf Spot

This is a type of disease that is caused by the parasitic algae Cephaleuros virescens.

It affects not only the leaves but even the twigs of your calathea. The spots would look like patches that may be green-gray or greenish-brown in color. 

The leaves of the calathea may even turn yellow and drop in advance. It happens when the leaves get heavily infected. (Source: Clemson University)

Fungal Diseases

One possible reason for the brown spots present in your calathea is a fungal disease. Here are the common fungal diseases that can infect your calathea plants:

  • Alternaria Leaf Spot 

This disease is caused by the fungus known as Alternaria alternata. Infected calatheas will show small spots that are water-soaked in appearance. They look like reddish-brown lesions on the leaf surface. 

  • Helminthosporium Leaf Spot 

Caused by Drechslera setariae, this type of leaf spot disease causes the leaves to develop water-soaked lesions.

The spots are initially yellow but later turn brown. Through time, the small spots join together and create bigger marks on the leaves. 

  • Fusarium Wilt 

Calathea plants infected with fusarium wilt will show wilting and yellowing of the lower leaves.

This is because the base of the plant where it was cut dies and rot.  Fusarium oxysporum is the pathogen behind this disease. 

Anthracnose

If you notice that the calathea leaf tips are yellowing and then turning tan then brown, it probably is a disease known as anthracnose.

The browning in the leaf tips extends on the entire leaf until it totally dies. Colletrotrichum and Gloeosporium are the fungi behind this disease. 

Wounded plants are more susceptible to anthracnose fungi. If you’ve used a previously infected tool, the chance to transfer the disease-causing agent is high. 

Septoria Leaf Spot

Septoria leaf spot often affects the lower and older leaves of your calathea plants.

Generally, the leaves would appear yellow to brown. Affected leaves will eventually wither and die. 

When you look closely, calathea leaves have small brown spots that have a white center. 

Powdery Mildew

One distinct thing you’ll observe with calathea leaves infected with powdery mildew is the presence of a powdery white texture.

At times, the leaves would have a brown and papery texture. This is caused by the pathogen known as Oidium species. 

This pathogen can transfer from the decaying materials present in the soil to the plants. They can also travel through the air. 

Bacterial Leaf Spot of Calathea

Bacterial leaf spot on calathea may be caused either by P. cichorii or Pseudomonas sp. These bacteria affect the leaves of particular species such as C. roseo-picta and `Vandenheckei’ as well as C. roseo-lineata.

The lesions are water-soaked in appearance with tan to brown color and may have a size of 1-inch in diameter.

The symptoms of Pseudomonas sp. are mostly seen in younger leaves. The P. cichorii affects the older leaves of calathea. They tend to enlarge when the wet condition persists.

Nutrient Deficiency

The lack of any essential nutrient causes the leaves to develop chlorosis and/or necrosis.

Chlorotic and/or necrotic leaves initially appear as yellow while others develop brown edges.

The symptoms will depend on the type of macronutrient or micronutrient that is lacking.  

  • Mobile nutrients such as nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) will express its symptoms on the lower and older leaves. 
  • On the other hand, immobile nutrients like calcium (Ca), boron (B), chlorine (Cl), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), silicon (Si), sulfur (S) and zinc (Zn) will show symptoms on the younger leaves. 

Edema

Edema is a physiological response that a plant does to certain environmental factors.

It is related to uneven water relations inside the plant. As a result, certain plant parts such as leaves, stems, and petioles develop protrusions. 

The damaged parts would have blister-like structures on their surface. These blisters rupture and develop into brown lesions later. 

Excess Light or Leaf Scorching

Calathea requires medium exposure to sunlight. A low light condition can cause the leaves to turn pale and weak.

On the other hand, excess light leads to tip necrosis and even bleaching. Higher levels of light can burn the tissues of your calathea.

It then leaves brown markings on the surface of the leaves as a result of scorching. The colors also fade as the leaves experience bleaching. 

Frost Damage

A temperature range of 65°F to 80°F (15°C to 27°C) is ideal for your indoor calathea.

Generally, they’re not tolerant of cold temperatures. Thus, they get easily damaged with frost. 

When the temperature gets too cold for the calathea, the tissues can freeze and die.

Once thawed, you’d see brown spots appearing on the leaves. The frost damage on calathea leaves is irreversible. 

Low Humidity

The calathea plant surely loves that extra moisture present in the air. This means that it requires a highly humid environment in order to thrive.

It requires around 40% to 60% relative humidity to flourish and produce gorgeous leaves. When the air is too dry, calathea leaves will easily develop brown edges. 

Insect Infestation

Pests like mites, caterpillars, scales, and mealy bugs commonly bother ornamental plants like calathea.

They normally feed on the leaves puncturing the tissues and sucking the contents. The wounds left to develop into brown lesions. 

The presence of a few insects is not a serious problem. But, when they multiply and take over your plant, it will definitely give you a headache. So, don’t underestimate these pests when they appear. 

Watering Problems

Since calatheas would only need medium watering, there is always the tendency to overwater or underwater the plant.

Improper watering can either dehydrate or drown the plant. In both cases, the plant suffers from water stress and exhibits yellowing and/or browning of leaves. 

Overwatering leads to root rot. Underwatering can shrivel the roots due to dehydration.

As a result, the roots will have trouble transporting water and nutrients from the soil to other plant parts.  

Fertilizer Burn

One of the damages of excess fertilizer is the burning of the leaf tips or the scorching of the leaves.

You would often see brown tips forming on the edges of your calathea leaves.

The soluble salts from too many fertilizers create a drought condition on the soil by pulling away water from the roots. 

The lack of moisture in the soil results in wilting. Other times, direct contact with fertilizer may also lead to burning.

This can happen when the solution is not diluted to half or quarter of the original recommendation. 

How to Treat Brown Spots on Calathea Leaves? 

Once you are certain about the real cause of the brown spots on your calathea, it’s time for you to take action.

Here are the simple solutions that we can recommend to help treat brown spots on your calathea: 

For Brown Spots Caused by Diseases (Bacterial, Fungal, etc.)

  • Remove infected leaves and plant parts. Destroy them to avoid the spread of the disease. 
  • Isolate the calathea in a dry, warm, and well-ventilated place. 
  • No overhead watering. Keep the foliage dry as much as possible. A damp condition invites the growth and proliferation of pathogens. 
  • Apply appropriate chemicals such as fungicides (link to Amazon) depending on the causal agent of the disease. 
  • Destroy heavily infected plants. If the disease persists even after employing the above-mentioned management practices, it is time to finally let go of your calathea plant. 

For Brown Spots Caused by Nutrient Deficiency

  1. Identify which exact nutrient is lacking by subjecting the soil to analysis. You can send samples to a laboratory. However, this is a bit expensive especially if you are only concerned about one or two pots of calathea plants. 
  1. Consult with an ornamental plant expert. If you know a horticulturist, better ask that person to check on your plant. These people are surely more skilled in identifying nutrient deficiencies. 
  1. Check the soil pH and adjust it accordingly. One reason why nutrients become unavailable for plant use is that the soil’s pH is not at its optimal value. For calathea, the soil pH must be around 6. You can test this using a pH meter. (link to Amazon)
  1. Repot using healthy and more fertile soil. Perhaps the potting medium of your calathea is already depleted. In that case, you need to transfer it to another pot using a fresh set of soil. 

For Brown Spots Caused by Edema and Watering Problems

  • Water your calathea with a medium amount of water. Remember your plant is neither a heavy nor a less drinker. It needs just enough water to thrive. 
  • Always let the excess water drain from the pot to avoid root rot. Use pots that have enough drainage holes. Allow water to drain before putting it back in its original location. 
  • Adjust watering frequency depending on the season. If the temperature gets high, increase water frequency. Do otherwise when it gets colder. 
  • Don’t water in the evening. Your calathea will hold moisture longer because transpiration is slower during the night. Instead, water early in the morning. 
  • Ensure your plant is receiving enough light. Light emits heat and heat increases the transpiration process. Thus, your plant will easily lose moisture. 

For Brown Spots Caused by Excess Light/Scorching

  • Limit your calathea plant’s exposure to direct sunlight to around 2 to 6 hours daily. If light intensities are too strong, limit exposure to the minimum. 
  • Provide additional shade such as sheer curtains to serve as protection from harsh light intensities. Don’t allow your calathea to directly touch the window glass.  
  • Relocate your calathea to an area where light intensity is not that strong and destructive. 
  • If using artificial light sources, keep it at a distance of at least 12 inches away from your calathea. 

For Brown Spots Caused by Low Humidity

  • Place your calathea in an area that usually has high humidity. This includes your kitchen and your bathroom.
  • Regularly mist on your calathea when the air gets too dry. Use a spray bottle and mist around the foliage every morning. You can do this more than once a day if humidity gets too low. 
  • Turn on a humidifier if available. If you don’t have extra time to do misting, let the humidifier do it for you. Although, this will cause additional costs on your part. 
  • Group it with other plants. Plants that come in groups are better off because the moisture one releases can be absorbed by another. 
  • Use a water tray. This works well especially if you are to leave home for days or weeks. Allow your calathea to sit on a pebbled tray that’s half-filled with water. 
  • Use a bell-shaped dome to trap moisture. There are other gardeners who do this. It resembles the environment of a terrarium garden where humidity is maintained high by means of the glass container around it. 

For Brown Spots Caused by Frost Damage

  • Relocate your calathea plant to a warmer location during the night. Night temperatures are usually lower and it may cause frost to occur. 
  • Insulate your calathea when the seasons get cold. During winter, make sure to protect your calathea by providing an extra source of warmth around it. Cotton sheets will be fine to shield your calathea from the cold. 
  • Reduce watering when the temperature starts to drop. Excess moisture will cause the potting soil to freeze. Never water in the evening.
  • Provide enough light sources. Make sure your calathea is receiving enough light especially when it is cold. Add artificial light sources if needed. 

For Brown Spots Caused by Fertilizer Burn

  • Leach off excess fertilizer with water. Pour water into the soil repeatedly until the white crust is gone. Allow 1 to 2 hours in between to avoid damaging the roots.
  • Stop fertilizer application until the roots recover. Give your calathea the break it needs. 
  • Repot the calathea. If the salt build-up is already too much, better get rid of the potting soil and replace it with a new one. Use a fertile potting medium to ensure that all essential nutrients are present.
  • Use slow-release fertilizers. The reason why fertilizer burn happens is that we are more inclined to use readily available fertilizers. Although they have an immediate effect, they can easily damage the plant too if not handled well. 
  • Fertilize the soil, not the foliage. Direct contact with fertilizer solutions can easily burn the leaf tissues of any plant. Avoid doing this unless the fertilizer is intended for foliar application. 

For Brown Spots Caused by Insect Infestation

  • Manually remove the pests. You’d be lucky to catch them when they’re few if you are faithful to checking on them regularly. 
  • Spray water over areas where the colonies of pests have grown. Just enough pressure will be sufficient to drive away pests from the leaves and stems. 
  • Remove heavily infected leaves. If the damage is severe, better prune that part. This will prevent the pests from spreading. 
  • Use homemade solutions out of diluted horticultural oils and dishwashing/insecticidal soap to kill the insects. Do this whenever you see insects roaming around your calathea. 
  • Most of the time, there’d be no need to use chemicals. But just in case, opt to use organic and environment-friendly solutions. 

Treating brown spots in calathea is not a one-time activity. You have to be patient in employing the solutions over and over again until you see positive results.

There’ll be even times when you’d need to experiment yourself to find a better way to manage your calathea. 

How to Prevent Brown Spots on Calathea Leaves? 

Of course, brown spots wouldn’t appear in your calathea if you’re careful to provide the best growing conditions from the beginning.

So, here are some ways we recommend you do to prevent the recurrence of brown spots on your beloved calatheas. 

  • Start with a healthy, vigorous calathea plant. Always choose the best-looking calathea wherever you go visit and buy from garden stores. Never ever buy a diseased or unhealthy plant. 
  • Use sterilized potting mixes. This is to reduce the chance of developing soil-borne diseases. Pathogens have a way to stay alive in the soil for a very long time so heating the medium would kill them. 
  • Ensure proper potting mix. (Link to Amazon) Pot the calathea in a well-draining potting medium that is high in organic matter. Use peat, pine bark, vermiculite, and/or perlite as soil amendments. 
  • Use a pot that is of the right size and has good drainage. Too small or too large pots can cause watering problems. If drainage is not present, there’s a high chance that root rot will follow. 
  • Keep the foliage dry. Remember that a damp environment is very favorable for pathogens to grow and multiply. 
  • Find the best location. It should be one that receives enough light, has high humidity, and is warm during the night. Keep your calathea away from drafty locations. 
  • Manage your watering. Never too much but never too little is the drill for calathea. Check the condition of the soil before watering. Allow the top 2 inches to dry out first. 
  • Always dilute fertilizers. Calatheas have a very poor tolerance for salts. They can easily develop fertilizer burns so be careful with your fertilizer application. 
  • Be mindful of the changes in temperatures. When it hits lower than 60oF (15oC), be prepared to protect your calathea from frost. Provide insulation before it’s too late. 
  • Never be afraid to get rid of calatheas that are already in bad shape. Sometimes, letting go is the best thing to be able to save what’s left. This is true, especially with diseased plants.
  • Regularly check on your calathea. Treat them like your babies. This will give you the chance to spot any problem before they blow up into something really serious. 
  • Double-check your plant before bringing it inside your home. Moving your calathea outdoors is beneficial to the plant. But, make sure that you check them for any presence of pests before you bring them inside again. 
  • Keep the growing conditions at its best as much as possible. Surely there are changes that happen in our environment that we can’t control. As a plant parent, it’s your responsibility to find ways to keep your calathea as safe as possible. 

Final Words

Generally, taking care of a calathea plant will require more effort than with other indoor plants. It is considered as a high maintenance houseplant. This means that you can’t be procrastinating when it comes to tending a calathea. 

But what it requires for care and maintenance, it compensates with its beauty. Give the calathea what it needs and it will never disappoint you. The stunning leaves that it will parade will be your greatest prize.