5 Reasons For Mint Leaves Turning Black[Causes & Treatment]

Mints are one of the most popular herbs around the world. Whether it’s a mojito or a nice cup of tea, mints upgrade the flavor with their beautiful aroma. 

But these bushy green herbs can fall victim to some stress conditions and start to turn black. With your little help, the black leaves of your mints can be healed back to normal. 

However, without knowing the proper reason you cannot just start to treat the plants. Because wrong treatment can make the condition even worse.

So, why are the mint leaves turning black?

Watering problems, Incorrect Soil, Environmental Stress, Diseases, and Pest Attacks are the 5 big reasons for making your mint leaves turning black.

No need to worry! This article has got you covered. Here I am going to talk about the 5 reasons for the black leaves of the mints with their specific treatments.

So let’s get down to business-

Why Are The Mint Leaves Turning Brown?

1.Watering Problem

Water stress is one of the major reasons behind mint leaves turning black. Mints have a delicate root system. The roots cannot function properly in waterlogged conditions. On the other hand, too dry soil can also create tension for the root.

So the bottom line is, when the drainage is not right the root quickly gets stressed. In this case, the mint leaves first turn yellow and then black.

A moisture meter (Our pick: Atree Soil Soil Tester Kits with Moisture, Light, and PH Test for Garden)can guide you to a good watering schedule 

Control Measures

First, remove the black leaves from the plant. Mints need moist soil but not too much water. So, inspect the soil with a moisture meter before watering. You can also check the moisture with your fingers by dipping them in the soil.

If the weather is very humid then water at 3 or 4 days intervals. If the weather is moderate then water once a week or 10 days. Make sure you are watering the right amount depending on the soil condition of your plant.

For potted mints, keep enough drainage holes. Mints have exposed roots. So, when the plant grows more, repot them in a larger pot to give them some extra space.

2.Incorrect Soil 

Since Mints have a very delicate roots system they prefer light and well-drained soil. Compact and dry soil even encourages other diseases. So the soil needs to be fertile and loamy for your mints.

The advantage of light soil is, it also provides good drainage and ensures better nutrient uptake.

Over-fertilization also creates an imbalance in the soil. Overdose of fertilizer causes burns in the leaves. It can result in mint leaves turning black and curling up. 

There is one more issue. Due to over-fertilization sometimes salts can accumulate on the soil surface. And the Mint plants are not salt tolerant. In this case, the soil will look whitish from the surface. This can also make the edges of your mint leaves turn black and crispy. 

If the soil pH is below 7 then there can be salt present in high concentrations. So before adding any fertilizer check the soil pH with a pH meter. 

Control Measures

As we eat mint leaves directly from the plant make sure you don’t use any chemically toxic fertilizer. Apply the best fertilizer to your mints that are specifically made for herb plants (our pick: Jobe’s Organics Herb Plant Food)

To improve the soil the best thing you can do is add organic compost or perlite (our pick: Miracle-Gro Perlite) This will help maintain good moisture in the soil and provide enough nutrients for mint growth.

If you have potted Mints in the same pot for several years then repot them in fresh soil (our pick: Espoma Organic Potting Mix). It’s better to use clay pots than plastic pots for good drainage.

To remove the salt accumulates, remove the top few centimeters of surface soil and replace them with fresh soil.

3.Environmental Stress

Mint plants are very quick to grow when they get a fair amount of sunlight. But when the temperature goes above 30°C or 85 °F the plant suffers from stress. High temperatures can dry up the mint leaves and turn them black.

Ironically, when the mint gets too bushy the lower leaves can slowly turn black for lack of proper sunlight. 

Control Measures

Cut off the black leaves from the plant. Make sure both lower and upper leaves are getting 6-7 hours of sunlight but not more than that. When the weather is too hot and humid make arrangements for afternoon shade. 

Sometimes it can be hard to manage these environmental conditions. But the good thing is you can bring your precious outdoor mints indoors and put them under Indoor grow lights.

4.Disease of Mint

Mint Rust, Leaf Blight, Verticillium Wilt are the three fungal problems behind mint leaves turning black. All these fungal attacks occur in cool and damp weather.

Mint rust makes the leaves turn yellow with small black spots. Leaf blight turns the entire leaf black. And Verticillium Wilt does the same thing along with twisting and curling the leaves.

Control Measures

First, cut down the infected black leaves. Then you need to apply a fungicide that will not have any toxic effect on the mints. The fungicide that lets you quickly harvest after its application is the best for your mints (our pick: Bonide Copper Fungicide)

Make sure the infected leaves are safely thrown away without contact with other plants.

Here are a couple of natural home remedies that are very useful and effective against fungal attacks: 

# Recipe 1:- Baking Soda Spray Recipe

Ingredients

  • Baking Soda 2 teaspoon
  • 1 teaspoon of liquid soap
  • 2 liters of water

Steps

  • Mix the baking soda with water then add the liquid soap.
  • Spray thoroughly on both sides of the leaves.

#Recipe 2:- Vinegar Spray Recipe

Ingredients

  • 3 teaspoons of apple cider vinegar 
  • 2 liters of water
  • Few drops of liquid dishwashing soap

Steps

  • Mix the ingredients very well 
  • Spray on both sides of the infected leaves twice a week until the problem solves.

# Recipe 3:-Milk Spray Recipe

Ingredients

  • 1 liter of sour milk 
  • 1 liter of water 

Steps

  • Mix the milk and water and start spraying
  • It is a very effective remedy against the fungal problems
  • Don’t store it. Use it as an instant mixture 
  • Spray it twice a week until the problem stops.

Tip: In the case of all homemade recipes, always use a small part of the solution in a small area of a leaf. If the leaf burns or discolors then dilute the solution with water. And again apply to a small leaf.

Preventive Measures

Fungal problems occur mostly in damp and humid conditions. Keep proper planting space between plants for better air circulation.

If the plant is getting too bushy, prune off some old leaves. Water your mint plants in the morning. In this way, the extra water drops on the leaves have time to dry out in the sun. Water the plants only when the soil gets dry.

In the case of potted mints, change the potting mixture if you suspect fungal growth. Keep any other infected plants separated from your mints. During winter bring the mint plants indoors if possible. 

5.Pest Attacks on Mint

If you can’t relate to the above reasons and are still wondering what else is the cause for your mint leaves turning black? Then the pesky pests are the reasons that are feeding on your mints.

Mints are often attacked by aphids, cutworms, thrips, and spider mites. They feed on leaves and create brown and black spots. Aphids are the most attacking pests on mint. Their severe attack makes the mint leaves black and eventually the plant can even die.

These pests are usually very tiny and hard to notice. So look for movements on the leaves and check the lower side of the leaves every once in a while.

Control Measures

Give your mints a moderate spray of water to wash off the pests. But when a massive attack of these pests happens you must use an insecticide. It is very important to kill the pest because they cause other severe diseases to the plants.

But now the question is what insecticide to use. Well, we mostly eat the mints freshly from the garden in salads and drinks. So applying any type of insecticide is not a good idea. Apply the best organic insecticide on your mints so the leaves are safe to eat (our pick: Monterey Garden Insect Spray)

For other ways of organic control, you can spray neem oil and insecticidal soap (our pick: Natria Insecticidal Soap).

Some natural homemade recipes can also help you control pests. Check out these below:

#Recipe 1:- Horticultural Oil Recipe

Ingredients

  • 3 teaspoons of liquid dishwashing soap 
  • 1 cup of any oil like olive oil or vegetable oil. 

Steps

  • Mix these ingredients very well and store them as a stock mixture in a bottle.
  • Add 1 tablespoon of this mixture with every cup of water and pour it into the sprayer.

#Recipe 2:- Basil Tea Recipe

Ingredients

  • 1 Cup of fresh basil
  • 1 teaspoon of liquid soap
  • 3 cups of water

Steps

  • Boil the water and then remove it from heat
  • Add the basil leaves and cover the pot with a lid.
  • Keep the lid closed and wait until the water cools down 
  • Then strain the basil leaves from the water.
  • Lastly, mix the liquid soap and put the mixture into the sprayer
  • Spray it twice a week.
  • It’s very effective against aphid infestation.

#Recipe 3:- Tomato Leaf Spray Recipe

Ingredients

  • 1 cup of chopped tomato leaves
  • 2 cups of water

Steps

  • It’s very easy. Soak the chopped tomato leaves overnight in 1 cup of water 
  • After that, Strain out all the tomato leaves and add another cup of water to dilute the solution. 
  • Spray on the leaves twice a week. 

Preventive Measures

Do not over-fertilize the soil. Maintain good soil moisture because spider mites attack in dry soil conditions. Don’t apply insecticides during very hot weather. This can also burn the leaves and turn them black.

Encourage beneficial insects such as ladybugs and lacewings into your garden. Because they feed off these harmful insects and don’t do any additional damage to the plants.

Frequently Asked Questions (FAQs) 

Can I eat black mint leaves?

If the black spots are caused by fungal disease then you cannot eat them. But if the black leaves are due to water or heat stress then you can eat them after treating them properly.

Can I eat mint leaves that have holes in them?

It’s probably not a good idea to eat the leaves with holes

You can eat the leaves if the insects have caused them. But if it is due to disease or animal damage then you should not eat them. Throw them in the garbage.

Conclusion

Mints are very delicate plants. They need all the care they can get especially if they are under stress. So when you see your mints are turning black then don’t make any delay. Revive your plant with proper care, apply good fungicides and insecticides. 

In this article, I’ve tried to explain why the mints are turning black with their solutions. I hope this writing helped you to fix the black leaves on your mints. 

Don’t forget to share with us your experience with the delicious mints. If you have any further questions ask away in the comment section below.

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