Understanding the causes of why mint leaves turn black

Mint is a versatile and fragrant herb, you can eat mint leaves by using them in cooking and as a garnish in drinks.

However, many gardeners and mint enthusiasts may have come across the issue of mint leaves turning black. This can be a concerning and unsightly problem, but the good news is that there are a few reasons why this may happen and steps that can be taken to prevent it.

In this article, we will explore the causes of spots on healthy leaves and provide solutions to keep your mint leaves looking healthy and vibrant.


We will also discuss proper care and maintenance techniques to ensure that your mint plant receives the right amount of sunlight, water, and nutrition to thrive.

Reasons why mint leave turns black

Mint is a popular herb used in many dishes and drinks, but it can be concerning when the leaves begin to turn black.

There are several reasons why this may happen, and understanding the cause can help to prevent it from happening again in the future.

Fungal infections

Fungal infections, such as anthracnose or leaf blight, can be a common cause of black spots on mint leaves.

Leaf blight

It is a fungal disease that can affect mint. It is caused by the fungus Phytophthora methane, and it typically results in dark brown or black spots on the leaves of the plant. These spots can vary in size and shape and can appear on both the upper and lower surfaces of the leaves.

The leaf blight fungus can survive in soil and plant debris, and it can infect plants at any stage of their growth.

High humidity, overcrowding with other plants, and poor air circulation can contribute to the development of this disease.

Symptoms may begin to appear as early as the seedling stage and can continue through the growing season, leaf blight can cause the leaves to wilt and fall off, thereby weakening the plant and reducing its productivity.

Mint rust

Mint rust is a fungal disease that can affect mint. It is caused by the fungus Puccinia menthae. The fungus infects the leaves, stems, and flowers of the mint plant. Mint rust appears as small, yellowish, or bright orange spots on the leaf’s underside.

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The leaves can become deformed, twisted, or curled, and in severe cases, the entire leaf may turn yellow and drop prematurely.

The mint rust spores can also spread to other parts of the plant.

Mint rust is most commonly found in humid, wet conditions and can survive in soil and plant debris. The disease is a common fungal disease in regions with high humidity and rainfall. The fungus can infect the plant at any stage of its growth, and it can cause significant damage to the mint that could happen to orchid flowers as well.

Exposure to too much sunlight

Exposure to too much sunlight can cause spots on mint leaves as they only require light shade. Mint plants prefer partial shade and too much sun can cause damage to entire leaves, leading to black spots.


This can happen when a plant is grown in a location that receives full sun for most of the day, or when the plants are grown in a greenhouse or indoors near a window that receives direct sunlight.

The signs of too much sun exposure are often visible on the leaves of the mint plant. Leaves may turn yellow or brown and will have black spots or patches. In some cases, the leaves may also become dry and brittle.


Overwatering can harm healthy mint leaves as it can lead to a soil that is waterlogged and prevent the roots from getting enough oxygen. This can cause damage to the roots and the leaves, leading to black spots on the leaves.


Overwatering can happen when the soil is too dense, when the mint is grown in containers without proper drainage, or when the plants are watered too frequently.

The leaves may become limp or wilted, or even fall off the plant. The stems may also become discolored and the plant may appear stunted.

Lack of proper nutrition

Lack of proper nutrition can cause defects in mint leaves. Mint plant requires a consistent supply of essential nutrients, such as nitrogen, phosphorus, and potassium, to stay healthy.

When the plants do not receive enough of these nutrients, or when they receive an imbalanced diet, it can lead to deficiencies, discoloration, and black spots on the leaves.

Environmental stressors

Environmental stressors such as extreme temperature fluctuations, drought, or extreme humidity can cause defects in mint leaves.

Mint plant is relatively hardy, but they can be sensitive to changes in the environment.

Extreme temperatures, either hot or cold, can cause damage to the leaves and lead to black spots.

Drought can cause excessively dry soil, which can cause the leaves to wilt and become discolored. Extreme humidity can lead to fungal growth and rots around the base of the plant.

High humidity

High humidity can cause black dots on mint leaves by promoting fungal growth around the base of the plant. It can create a breeding ground for mold and mildew, which can attack the mint plant and cause leaf discoloration, wilting and black spots.


In addition to leaf discoloration, black spots, and wilting, you may also see mold or mildew growing around the base of the plant.

Mechanical damage

Mechanical damage can cause black dots on mint leaves. This type of damage can occur when mint is squashed or hit by some other object.

It can also happen when the mint grows in an area with high traffic, or when the plants are grown close to other plants or objects that can brush against the leaves.

The impact can cause damage to the cells of the affected leaves and leads to the formation of black or dark spots.

The signs of mechanical damage on mint leaves are visible as black or dark spots, bruises, or other discolorations on the leaves. The extent of the damage can vary depending on the severity of the impact, but it can result in the partial or total destruction of the leaves.

Pesticide injury or chemical burn

Pesticide injury or a chemical burn can cause damage to leaves. This type of damage can occur when pesticides or other chemicals are applied to the mint at an improper rate or at the wrong time, or when the mint is exposed to chemicals or pollutants present in the environment.

Pesticides that are not labeled for use on mint or are used improperly can cause severe damage to the leaves, leading to dark spots.

The signs of pesticide injury or chemical burn on leaves are visible as black or dark spots, the leaves may turn brown, wilting, or even fall off.

The damage can vary depending on the type and strength of the chemical and the timing of application. In severe cases, it can affect the plant completely so its leaves get curled or distorted.

Pest infestations

Pest infestations, such as spider mites or mint aphids, can also be a cause of black spots. Mint Aphids are small, soft-bodied insects that can infest plants.

They feed on the sap of the plant and can cause damage to the leaves, stems, and flowers. Mint aphids can also cause discoloration and curling of the leaves of infected plants, and they excrete a sticky substance called honeydew that can attract ants and lead to the growth of sooty mold.

One of the most obvious signs of a pest infestation is the presence of small, dark spots on the leaves.

These spots may be accompanied by stippling or discoloration of the leaf tissue, and in some cases, you may be able to see the mint aphid themselves or their webbing.

Treatments for black spots on mint leaves

It can be caused by a variety of factors, including fungal infections, pest infestations, exposure to too much sunlight, overwatering, lack of proper nutrition, and environmental stressors.

Most factors except fungal and pest infections on a mint plant can be treated by following the proper cultural practices, such as using the right soil, monitoring the moisture, and sun exposure.

Treating an infected plant requires identifying the underlying cause and taking appropriate action. Here are common treatments for black spots on mint.

Fungal disease treatment

If you suspect that your mint plant is infected with anthracnose, it is important to take action quickly to prevent the fungus from spreading to nearby plants. Remove and dispose of any infected leaves and mint stem to reduce the number of fungal spores in the area.

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Mint rust can be treated with fungicides. Be sure to choose a fungicide labeled for use on your mint plant, and follow the instructions carefully.

Additionally, proper sanitation is crucial in preventing the spread of mint rust. Removing infected leaves and burning them or disposing of them in sealed bags to reduce the chance of spore spread.

Pests treatment

In terms of pest control, you can use a variety of methods, depending on the type of pest that you are dealing with. For example, insecticidal soap or horticultural oil can be effective against a mint aphid and spider mite.

Neem oil can be effective against a wide range of pests and will also help to control fungal infections. Always follow the instructions on the label and be cautious of overuse as neem oil can cause damage to the mint plant or the environment.

Additionally, encouraging beneficial insects such as ladybugs and lacewings can be a great way to control pests on your mint. A healthy ecosystem is more resistant to pests and will help to keep the mint healthy.

Prevention measures

  • For fungal infections

To prevent mint rust, it is important to provide the plants with good cultural care and sanitation practices.

Provide the plants with adequate air circulation, keeping the foliage dry, and watering the soil, not the leaves. It’s also a good idea to avoid over-fertilizing the plants, as this can lead to lush, dense growth which can promote fungal infections.

  • Pest infestations

It’s important to maintain good cultural practices. This includes providing the mint with adequate air circulation and keeping the foliage dry. Also, regular inspection for pests and identifying them is important, as acting on them quickly.

  • Sun damage

It’s important to provide them with partial shade, especially during the full sun. Placing mint under a shading structure or a tree or bush can help to reduce the amount of direct daylight they receive.

Also, In indoor mint, you should move them away from direct sunlight.

In addition, it’s also a good idea to move the mint plant from sunlight during the hottest part of the day. It will help the plant to adjust and protect it from sunburn and sun damage.

  • Nutrient deficiencies

Provide the plants with a balanced diet. This can be done by applying a balanced fertilizer, such as a 10-10-10, at planting time and every six to eight weeks as the mint grows.

It’s also important to monitor the pH level of the soil. Mint prefers light soil that is slightly acidic, with a pH range of 6.0 to 7.0. If the pH is too high, the plants may not be able to absorb essential nutrients, even when they are present in the potting soil.

  • Potting mix

Using the appropriate potting mix can help to prevent spots on mint leaves.

A well-draining potting mixture that contains a balance of organic matter, such as peat moss, vermiculite, or perlite, and coarse materials like sand or pot with drainage holes can help to ensure that the mint plant receives the proper amount of moisture and air circulation.

Regularly monitor the humidity and air circulation of the area where the mint plant is grown. Using proper drainage methods, like using a saucer or pot with drainage holes, can help prevent water from sitting on the soil for too long.

  • Environmental stress

To prevent environmental stress on mint plants, it’s important to provide them with the right conditions. Mints prefer slightly cooler temperatures and moderate humidity, so it’s important to keep them away from extreme temperatures, both hot and cold.

Also, it’s important to keep the mint plants out of the direct sun during the hottest part of the day.

  • Watering

The mint plants need consistent moisture, especially during periods of drought. Mint plants require consistently moist soil to keep your plant healthy, and when the soil becomes too dry, the leaves can become stressed and become discolored.

In terms of humidity, proper ventilation is important, as well as providing appropriate air circulation around the mint plants. Also, it’s important to keep the area around the mint plants clean and free from debris and weeds, as this can reduce the risk of fungal growth.


In conclusion, many factors can cause black spots on mint leaves, including fungal infections, pest infections, exposure to too much sunlight, overwatering, lack of proper nutrition, environmental stressors, high humidity, mechanical damage, and pesticide injury or chemical burn.

Understanding the causes of it is essential for preventing and treating the issue. Proper care, regular monitoring, and appropriate measures can help to keep mint plants healthy and prevent the formation of black spots on the leaves.

It is important to note that in case of severe damage, it might be better to remove the affected plant and start a new one. Consultation with a horticulturist or an agronomist can provide more specific advice on prevention and treatment.


Can you use black mint leaves?

It depends on the cause of the black spots, if they are caused by a disease or pest it would be best to discard the leaves and not use them.

If the black spots are due to environmental stressors or lack of proper nutrition, the leaves may still be safe to use, but it is best to discard any that have visible spots.

How do you fix black leaves on plants?

The method for fixing black leaves on plants will depend on the underlying cause of the problem.

Common methods include providing the plant with proper care, such as appropriate sunlight, moisture, and nutrition, removing damaged leaves, and preventing pests and diseases from infecting the plant.

Why is my mint getting black spots?

Black spots on mint can be caused by a variety of factors such as fungal infections, pest infections, exposure to too much sunlight, overwatering, lack of proper nutrition, environmental stressors, high humidity, mechanical damages, and chemical injury or fertilizer burn.

Why do mint leaves turn black in water?

Mint leaves can turn black in water due to a buildup of bacteria or fungal growth in the water.

The mint leaves can also turn black if the water is not clean or if the water is stagnant and has not been changed. Additionally, they can also turn black when exposed to chlorine or other chemicals in tap water, or if the water is too cold.

Elizabeth Martin

I am one of the best chefs and I work in a very famous Washington DC restaurant. My main hobby is to complement different dishes with fresh herbs. Almost all of them are grown in my house.

1 thought on “Understanding the causes of why mint leaves turn black”

  1. I don’t have a garden, so several times I tried to grow mint in a flower pot and failed every time. The stems of the plant became long, but there were few leaves on them. I thought they didn’t have enough light. I moved them to the windowsill. But there was another problem. The stems of the plant became black and dry. In the end, I concluded that mint is a plant for the garden, and not for the apartment. Perhaps someone has good experience with this. I would be glad if you tell me.


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