Are your mint leaves turning yellow? It’s not fun, I know. Having fresh mint leaves during the spring and summer adds a little freshness to your life, but mint can come with quite a few issues that can cause the leaves to turn yellow.
What Causes Mint Leaves to Turn Yellow?
Mint leaves usually turn yellow due to watering issues, pests, and fungal diseases. Other likely reasons could be nutrient deficiencies, heat scorching, or limited space.
If your mint leaves are turning yellow, here are some common causes that might be impacting your plant.
Overwatering and Drainage Issues
Watering is one of the most subjective things in gardening, even though it might not seem that way. You just water your plant and it’s good, right?
Well, how much should you be watering? Should you water every day? What if it’s hot out, do you water twice a day or more?
Especially as a new gardener, watering is usually done too often and too much. But even experienced gardeners are playing some sort of guessing game with watering.
This is why overwatering your plants is one of the most common issues with mint of any kind. And it can cause a lot of problems, especially if you’re growing mint indoors in containers.
Using a good potting mix with well-draining soil is a great way to ensure moist soil, which is key for having healthy mint plants.
Overwatering your mint plant can cause root rot, yellowing or brown leaves, and weakened stems.
Underwatering Your Mint
You can also not water your plant enough. As you can probably expect, dry soil can lead to issues as well.
Mint needs water to grow and produce enough leaves for a great harvest. If you missed a few days watering your plant, I wouldn’t try and overdo it too much. Water it normally, then do that again the following day if it’s still dry.
You don’t want to drown the plant roots and make the problem worse. Check the soil surface regularly to see if it’s dry. You want to keep the soil moisture a little damp, but not as wet as a dripping sponge.
If the weather is really hot, surrounding soil with organic mulch and help with water retention and keeping the soil moist even when it’s extremely hot out.
Heat & Sunlight
While you might think that all plants prefer as much sunlight as possible, mint is not one of those plants. Mint prefers to get some shade in its life, but it also needs sunlight, so don’t give it too much shade.
Mint gets something similar to sunburn if you leave it in the sun too long, or transplant it too early without going through a hardening-off period.
Mint sunscald is what that “sunburn” is called. The mint leaves will turn white and yellow, kind of like the picture below.
If it’s too hot outside, a similar issue can happen and the leaves will turn brown or yellow. If you have to keep your mint in full sun, make sure you check the soil regularly to see if your plant needs water.
Try using shade cloth to help reduce the amount of heat and sunlight your plants are getting on those really hot days.
When a plant doesn’t have enough room to grow properly, the roots become what’s called “rootbound“. This is an issue commonly seen with potted plants, or those in containers. Oftentimes, when you buy a seedling from a nursery or big box store, the roots will look like this.
Rootbound plants are easy to spot once you pull the plant out of its container. The root ball will have no more room to grow.
But if it’s still in the container, check the drainage holes. Oftentimes, the roots will try to escape through those holes when they have no more room in the pot.
Mint leaves will start to turn yellow when the plant is rootbound.
How to Fix a Rootbound Plant
You can usually fix this issue by massaging the roots until they are not as compacted. Then, repot the plant in a larger container with enough drainage holes.
Pests on Mint Plants
Aphids are commonly called little green bugs, but they do come in all colors. They are very small and can be harder to see until you notice yellowing leaves.
Aphids usually live on the bottom side of leaves, so unless you’re checking them regularly, you might miss the issue.
Mint aphids (ovatus crataegarius) can damage the plant leaves with a sticky, brown or clear liquid they leave behind called honeydew. Honeydew can attract fungal diseases to the plant such as sooty mold.
How to Get Rid of Aphids
Getting rid of aphids completely can be a challenge. Spraying neem oil on your plants every 1-2 weeks can dramatically help the issue. Beneficial insects like ladybugs can also help as they love to munch on some aphids.
Spider mites are another issue that can impact most plants. They spin webs on the leaves that might initially look like a typical spider, but as the population grows, they can weaken or even kill the plant as they feed on the juice in the leaves.
If you start noticing cobwebs on your plants, you probably have a spider mite problem. Catching them early is critical to avoiding a large population of them taking over your mint.
How to Get Rid of Spider Mites
Spider mites thrive in dry, hot weather, so if you give your plant the shade that they enjoy, you can mitigate the issue. You can spray them with your watering wand or hose to provide enough pressure and get them off the plant.
Companion planting mint with carrots and daisies can also help as they attract predatory insects that feed on spider mites.
Four-Lined Plant Bug
Four-lined plant bugs (yes, such a creative name) LOVE the mint plant and other herbs in the mint family.
They will suck the plant juices out of the leaves and cause some pretty serious damage. Although it’s mostly cosmetic, they’re still ruining some of the leaves you could have made a delicious mojito with!
The four-lined plant bug can move fast and cause a lot of damage in just a few hours.
Their eggs start to hatch in the spring and the nymphs feed on the top side of mint leaves.
The females lay their eggs on the top 4-5 inches of mint pants so you should be able to find them easier. If you do find them, you can knock them into a jar of soapy water.
How to Get Rid of Four Lined Plant Bugs
Neem oil and insecticidal soap can help mitigate the issue. Because they appear and cause damage quickly, neem oil is a good preventative option to keep them from starting this fast, yet destructive process in the first place.
Spray it on the foliage of the mint plant every 1-2 weeks to keep pests away.
Mint has a few common fungal diseases that can wreak havoc on your crop and harvest. The most common is mint rust.
Mint rust is a common problem and can cause yellow leaves that have rusty-looking spots on them. It’s caused by too much humidity and moisture on the leaves, which happens when they stay wet for too long.
Mint rust shows up as brown spots on the leaves that have a yellow ring around them.
How to Prevent and Fix Mint Rust
Prevention is really key here. By watering your mint at the base of the plant (not from above) you avoid getting the leaves wet altogether. Without wet leaves, it’s going to be far less likely that your mint will suffer this fungal disease.
Good air circulation is another key factor in prevention. If you have multiple plants in one large pot, it can be hard for the mint plants to get good airflow. Make sure each plant has enough space to “breathe” and get fresh air on the regular.
If you have mint rust, you want to move quickly. Cut the infected leaves that have rust spots off the mint plant. Since they have a fungal disease, I wouldn’t compost them and I definitely wouldn’t eat them.
Make sure you give the plant enough room to breathe and stop watering the leaves, water the base of the plant. Bottom watering is another way you can get your plant water without possibly introducing fungal issues.
Blight is a type of disease that comes in many forms and can impact almost any plant. Blight can kill the entire plant, cause stunted growth, and can turn the leaves different colors.
It generally impacts the main stem but can also appear in the lower leaves of the mint plant.
It forms a bull’s eye pattern of small brown spots with rings around them. If left for a long time, the plant and leaves will start to turn yellow and the plant can die.
How to Fix Leaf Blight
Copper fungicides work to get rid of blight and issues like powdery mildew.
Prune off the infected parts of the plant and make sure to clean your pruning shears between uses to avoid spreading diseases. This is a good idea even when regular pruning or gathering a harvest.
Tomato Spotted Wilt Virus
While it’s called the tomato wilt virus, this impacts mint plants as well. This virus is spread by thrips, a common pest of the mint plant. Thrips will spread this disease from other plants like tomatoes, grapes, strawberries, and even soybeans.
This will cause leaves that are brown or orange in color. The leaves may even start turning a silver color or black due to thrips fecal matter.
How to Fix Tomato Spotted Wilt Virus
Prune all damaged leaves and spray the entire plant with 2 teaspoons of dish soap per gallon of water.
You can also use a spinosad spray which can help take care of thrips, caterpillars, and leaf miners.
Can You Eat Yellow Mint Leaves?
If your mint plant is infected with rust or another fungal disease, you should avoid eating the leaves. If your plant has mint sunscald (i.e. sunburn) you can eat the leaves, but they might taste a little off.
Pruning your mint plant to get rid of the yellow leaves should help with air circulation and increase the health of the plant over time.
No one wants to find yellow leaves on their mint plant, but now you’ll know some ways to get rid of the issue and help your plants grow large and provide a better harvest.