I like to grow mint in my herb garden because it has a vibrant look, smells wonderful, and I can use it in my food. But I found some leaves turning brown and was worried.
Your mint leaves are turning brown because of a lack of water. You’ll find the leaves wilting and turning try. The mint leaves can turn brown due to overwatering if the root rot has set in. It may also turn brown when pests such as aphids, thrips, whiteflies are sucking sap from them.
I’ve written a lot more details about this problem and what you can do to fix your mint plant to make it healthy again.
Why Are My Mint Leaves Turning Brown?
Sometimes the reason behind an ailing mint leaf can be found by taking a closer look at its symptoms.
1. Overwatering the mint plant
The most common reason could be overwatering, where the soil remains moist and the roots cannot breathe.
This means the roots cannot absorb nutrients from the soil, causing the mint leaves to turn brown.
The symptoms of overwatering look similar to underwatering, and you may be tempted to continue watering the plant. And eventually, the mint plant will die as fungal problems like root rot will take place.
So, I recommend checking the moisture in the soil before watering the mint plant. It’s a simple, easy check where you stick your finger 2-3 inches into the soil.
If your finger comes out dry, that’s the time to give a good watering to the mint plant. If there’s soil sticking to your finger, there is sufficient moisture and you want to avoid the watering until it dries out.
One of the most common reasons for browning mint leaves is overwatering. Mint plants prefer soil that is evenly moist but not waterlogged. If the soil is consistently wet or the plant is sitting in standing water, the roots can become oxygen-deprived and begin to rot. To fix this issue, reduce the watering frequency and ensure the soil has proper drainage. – Diana, Gardener, The Gardening Talk
2. Underwatering the mint plant
As mentioned above, it’s possible to overwater mint. However, they prefer moist soil. So the other problem could be that you’re not providing sufficient water to the mint plant, causing the leaves to turn brown and brittle.
The symptoms of underwatering and overwatering can seem similar. But the simple check I provided above works well to recognize underwatering as well.
Stick your finger 2-3 inches into the soil and take it out. If the finger comes out dry, you know it’s time to give the mint plant a good watering.
Water the plant well whenever you need to water it. This helps the water reach deep into the soil and helps the roots grow long and strong.
3. Mint plant is receiving too much sunlight
The mint plant will prefer full sun for the best growth, but it also does not like too much heat as it’s a cold-season plant.
If the tips of the leaves are turning brown, there’s a good chance your mint is getting too much sun. You may also see the leaves curling up because of the heat as they try to conserve as much moisture as possible.
Try to grow the mint plant during a period of cool season such as the start of spring after the last frost date. Or when fall arrives, and the temperature drops.
If you end up growing mint in summer or the weather suddenly heats, you can cover the plant with a row cover to keep it cool.
If you’re growing the mint in a pot, it’s easy to move the plant to a shaded location. Or you could even move it indoors in the afternoon.
Mint leaves can turn brown due to too much heat or dryness. They do not like to dry out so maintain regular watering to help it thrive. Slightly acidic soil is ideal. To prevent leaf browning, make sure to provide adequate water and use a balanced fertilizer. – Sandra Nanka, Herb Expert and Nursery Owner at Mudbrick Herb Cottage
4. Mint plant is receiving less sunlight
The mint plant, like most herbs and vegetables, will require at least 6 hours of direct sunlight to grow well. The lack of sunlight could cause a lack of food and nutrients in the plant, causing the leaves to turn brown.
It’s easy to know if this is the problem by checking how much direct sunlight the plant is getting over the entire day. If it’s a few hours or only indirect light, you will need to move the plant to a better location.
It’s easy to move the plant if you’re growing the mint in a pot. If it’s in the ground, you’ll need to carefully transplant it to another appropriate location.
That’s why it’s better to plant this before starting the mint plant. Pick a location that gets the required 6 hours of direct sunlight to avoid this problem.
5. Mint plant is infected by fungal disease
Fungal disease can be a common problem, causing the mint leaves to turn brown. There can be different fungal diseases, but the cause is a humid environment.
We have already seen one type of fungal disease called root rot that occurs when the soil is overwatered, causing root damage.
There are other types of fungal diseases that will directly affect the mint leaves, causing discoloration. Two types of fungi just love mint plants are:
- Puccinia menthae, which causes fungal rust.
- Cephalosporium spp., which causes leaf blight.
Signs of fungal rust are orange, yellow, brown, and black spots on both the tops and bottoms of leaves. Leaf blight causes entire leaves to turn black or brown and fall off. This leaf disease is rare and usually strikes plants already weakened by fungal rust.
It’s easy to prevent fungal issues on the mint plant by avoiding humid conditions. Always water the base of the plant and prevent splashing water on the mint leaves. I prefer watering early in the morning so that even if there is excess moisture, it will evaporate as the sun comes out.
Make sure you prune the mint plant and there is no dense foliage that would cause air circulation issues and encourage humidity.
Environmental stress: Mint plants may experience stress due to extreme temperatures, drought, or over-watering. This can cause the leaves to turn brown and wilt. Pest infestations: Aphids, mites, and other pests can attack mint plants and cause the leaves to turn brown and wilt. Nutrient deficiencies: Mint plants may experience nutrient deficiencies if they are not being fertilized properly. This can cause the leaves to turn brown and wilt. Fungal infections: Fungal infections can cause the leaves of mint plants to turn brown and wilt. – Emily Jones, Gardener & Tomato lover, Tomato Mentor
6. Mint plant is infested with pests
Pests that attack your mint can cause all kinds of health problems for the plant, besides brown spots on leaves. Pests that commonly attack mint are:
Ants farming aphids on my pepper plants
A small, soft-bodied insect that is commonly found on the underside of leaves on many plants. They can vary in colors depending on the plant and can cause necrosis or stunted growth. Aphids also secrete a sugary and sticky substance called honeydew that can encourage the growth of sooty mold on plants.
It’s easy to get rid of aphids with water. Spray them till they fall into the soil and they won’t be able to get back on the plant. Spray the underside of the leaves as well.
Cutworms may be hard to diagnose because the larvae are usually active at night and hide in the soil during the day. They will eat holes through leaves and may leave young plants with stunted growth.
Cutworms attack many different herbs and vegetables, including mint, and can be prevented by checking all transplants and removing old plant residue before planting.
You can also put a small cone or collar around the base of the plant and hand-pick out larvae if possible.
If you have a thrips infestation, leaves will be speckled with black feces, and you may spot the tiny insect under a magnifying glass. Adult thrips are pale yellow or light brown while their offspring are lighter.
To treat a thrips infestation, avoid planting your mint next to plants such as onions that often attract thrips. An insecticide is recommended if the infestation becomes too vigorous.
The Two-Spotted Spider Mite causes leaves to be streaked in yellow or appear bronze coated. The mites appear as moving dots in the webbing or covering on the plants and are best viewed using a magnifying glass. They are small arachnids that can cause leaves to turn yellow and fall off the plant.
To prevent Spider Mites, dust around your plants and occasionally spray your plants with a strong jet of water if possible. Use insecticidal soap if the mite population becomes too high, but be careful of using many traditional insecticides as they can kill the mites’ natural predators and cause the pest to thrive.
In addition, make sure you clean all picked mint leaves thoroughly before consumption if you believe your plant may be affected.
7. Mint plant has constricted roots
This can be a problem when growing mint in a container. As the plant grows, the container may not be sufficient for the expanding roots and the plant gets root-bound.
This means the roots won’t be able to absorb the required nutrients from the insufficient potting soil, causing the leaves to turn brown.
The solution would be to move the mint plant to another larger pot as soon as you see the size has increased beyond the pot capacity. I would suggest growing the mint plant in a pot that is 12 inches deep to begin with.
This problem may also happen when growing the mint plant in soil if it’s too close to other plants. The roots may get intertwined with the other plant roots and suffocate.
Keep sufficient distance between the mint and other plants in the garden. Mint could get invasive and suffocate other plants as well. So I prefer to grow them in a container as the growth can be restricted.
8. Mint plant has grown old
Mint is a perennial plant, which means it will continue to grow every year for a few years. However, if the temperature drops beyond a certain point in winter, the plant will go dormant.
This would mean the leaves turn brown and fall off as the plant tries to conserve energy into the roots for the next growing season. This is completely natural and nothing to be alarmed about.
The mint plant will continue growing old as it grows every year, and there would be a time when the older leaves would turn brown and fall off. So if you have grown the mint plant for several years, it may be signs that its age that is causing brown leaves.
There’s nothing much you can do about an aging plant except let it mature and develop seeds that would encourage growth of new mint plants.
9. Mint plant does not receive required nutrients
Lack of nutrients, especially nitrogen, will affect mint plants and cause them to turn brown. This can happen because the soil is lacking the nutrients. Or the roots cannot absorb the nutrients even if present in the soil.
I recommend adding compost or some organic fertilizer like seaweed, blood meal, or fish emulsion every month to the soil. This ensures that the nutrients are present in the soil for the mint plant.
If adding nutrients to the soil is not helping, then this could mean the roots cannot absorb the nutrients. You need to find the root cause to fix this problem.
Overwatering can cause the roots to drown and be unable to absorb nutrients. Lack of water can also cause the roots to be unable to absorb nutrients.
Diseases are another reason that would affect the mint plant’s health and prevent it from absorbing the required nutrients.
10. Mint plant has been overfertilized
It’s important that the mint plant gets the required nutrients, especially nitrogen, to grow healthy leaves. But too much of fertilizer can also end up causing issues.
I don’t recommend using synthetic fertilizer, but if you are using it, follow the manufacturer’s instructions on the exact amount to use and how often. Otherwise, you risk burning the plant roots and causing a lack of nutrients instead.
Even if you use organic fertilizer, too much of it will cause excess foliage growth. The roots won’t be able to keep up and supply the required nutrients, causing the leaves to turn brown.
I suggest adding compost or organic fertilizer once every month after the plant has matured 4-6 inches in height. That should provide it with the required nutrients to grow sufficient foliage at an expected rate.
11. The soil has excess salt buildup
Tap water can contain salts such as sodium and magnesium that would build up over time in the soil. Hard water would also contain minerals that accumulate in the soil. Using fertilizers would also add some salts to the soil.
The problem with excess salt is the plant roots cannot absorb the required moisture and nutrients from the soil. This will lead to dehydration and the problems similar to underwatering.
The solution to this problem is to flush out the excess salts from the soil every few months. It’s easy to do this using a pure form of water, such as rainwater or distilled water. Give a thorough watering to the soil so it drains out from the drainage holes and removes the salts as well.
Is it Safe to Eat Brown Mint Leaves?
If your mint leaves have been properly picked and stored, then it is perfectly safe to eat browned mint leaves.
However, if your mint leaves have turned brown while still on the stem due to a possible fungus, then they are not safe to eat until you can cure your mint plant and restore the natural green color.
You also need to make sure that your mint leaves are not turning brown because of a toxic pesticide, as the poison makes your mint leaves unsafe to eat.
How do You Stop Picked Mint Leaves from Turning Brown?
Once picked, mint leaves will eventually turn brown as they lose nutrients and interact with the air. To best preserve the flavor and strength of your mint leaves once picked, wrap them in a slightly damp paper towel and then place them in a sealable bag or another airtight container.
If this method is not possible, try to store your mint in a way that keeps oxygen from reaching them and prevents them from drying out, such as in a sealed glass floating in the water.
Do Picked Mint Leaves Turn Brown in Water?
Mint leaves turn brown quickly when they are placed in hot water because they lose chlorophyll, which is the reason for their natural, rich green color.
They are still perfectly safe to eat and still provide flavor. However, if you place mint leaves in cold water, they will not turn brown and can be stored for a long period for future use.
Is it Safe to Eat Spotted Mint Leaves?
If the spots are because of insects, then it is safe to eat spotted mint leaves as long as they are thoroughly washed before consumption. It is also important to know if insecticides are being used to combat a pest, as they could make the leaves toxic.
If the spots are because of a fungus or disease, the leaves are not safe to eat, and the plant needs to be cured before consumption.