Mint has the well-deserved reputation for being a hardy, easy-to-grow herb. In fact, it spreads so readily that it can quickly become an invasive pest plant that takes over a whole garden bed!
But that doesn’t mean mint is immune from problems that can cause yellowed, sickly-looking foliage and stunted growth.
In this article, you’ll learn about 6 reasons for mint leaves turning yellow:
- Too much moisture
- Insufficient sunlight
- Insect attacks
- Nutrient deficiencies
- Fungal or viral plant diseases
You’ll also find out what you can do to bring back that healthy green color.
Let’s get to it and rescue your plants!
1. Too Much Moisture
This can occur for mint plants growing either in containers or in the ground.
With potted mint, there are two possible issues:
- You’re being overly generous in your watering
- Your pot has insufficient or blocked drainage
If you’re growing mint in the ground, the real issue is likely not your watering habits but rather your soil quality.
Clay is an absorbent material that readily retains moisture. If your soil has a high clay content, the water gets trapped in the shallow soil instead of draining downwards. Thus, your mint plant’s root system stays surrounded by water.
Whatever the situation, too much moisture can lead to three serious problems:
- Starvation. Your plant can’t absorb nutrients from the soil.
- Suffocation. Plants get a portion of their oxygen through their roots, and waterlogged soil blocks your mint’s breathing.
- Fungal overgrowth. Natural organisms that break down plant matter thrive in moisture. Over wet soil encourages these organisms to attack your plant’s root system, leading to premature rot and decay.
Rescue Plan: Water Less and Improve Drainage
For potted mint plants: Give water less frequently, and ensure you have proper drainage.
Always check soil moisture before you add any water. Insert your finger into the soil, and if it feels damp to your touch, wait a bit before watering. When the soil feels dry down to about your first finger joint, your mint is ready for a drink!
For proper drainage, only use a planter that has at least 2 drainage holes. Also, make sure the drainage holes aren’t obstructed in any way, either by clods of soil or by a flat surface under your planter. Especially if your planter is heavy or large, elevating it slightly creates an easy escape route for water.
For in-ground mint plants: Add organic matter to your soil to improve drainage.
Compost, well-rotted manure and last season’s finely-shredded leaves are excellent soil-enhancing organic material. If you want to learn more about soil health, check out this helpful resource from the University of Maryland.
Just be aware that building healthy, well-draining soil is a long-term strategy. You’re looking at a minimum of a few months before seeing any significant improvement in drainage quality.
For immediate mint rescue, transplant into better soil, be it in a container or another piece of ground.
We’ve just established that your mint can suffer from too much moisture, but a lack of water could also be to blame for yellow foliage.
When there’s not enough moisture to go around, your mint plant cuts off the supply to some outlying leaves to preserve the roots and main stem. Typically, the lower leaves are the first to wilt and turn yellow before they fall off altogether.
Your soil may be too dry if it feels dry to the touch and is crumbly, like this:
Rescue Plan: Give Your Mint More Water
If you suspect you haven’t been watering your mint enough, give it a long drink that soaks the soil.
If your mint is in a container, look for water to run out of the bottom. For plants growing in-ground, water until the surrounding soil is moist.
You may have to water a few times over a day or two to replenish the moisture levels your mint sorely needs.
3. Insufficient Sunlight
Like any plant, your mint uses photosynthesis to convert sunlight into usable plant food.
Chlorophyll, a nitrogen-rich substance is a key factor in photosynthesis, and it also gives your mint its beautiful green color.
This illustration is simple, but it shows that sunlight is a critical component of plant life:
Without sufficient sunlight to stimulate chlorophyll production, your mint plant can take on a yellowish tint as the green pigment dissipates.
Rescue Plan: Let the Sun Shine In
If you grow your mint indoors, make sure to use the sunniest window you have available. Also, make sure to turn your pot ¼ turn each time you water to give every leaf the sunlight exposure it needs.
A grow light is another great way to give your indoor mint plant the UV rays it needs.
It’s less common, but mint growing in the ground can still suffer if the sunshine is blocked by buildings, trees or shrubs.
Trim away any overhanging branches that may be in the way, and consider transplanting your mint into a sunnier location if you can’t eliminate the light-blocker.
4. Insect Attacks
In general, herbs aren’t frequent targets for garden pests, but a few may attack your mint and bring on yellowed foliage. Aphids and spider mites are the two most frequent offenders.
Aphids. These tiny bugs use their powerful sucking mouthparts to drain sap from your mint’s leaves, causing a sickly yellow hue to emerge. Make sure to look closely at your plant to spot aphids: They’re tiny and can be easy to overlook.
Here’s what to be on the lookout for:
Spider mites. Like aphids, spider mites feast on the sap from your mint plant’s leaves, leaving spotty yellow patches in their wake.
Spider mites are minuscule, and your first clue of their presence may be the wispy webs they weave. Be alert for this:
Rescue Plan: Use Insecticidal Soap
Not only does insecticidal soap effectively dispatch both aphids and spider mites, but it’s also a non-toxic product that’s safe to use on edible plants. (Still- make sure to wash your mint thoroughly before using it!)
You can buy either a ready-to-use spray formula or a concentrated one that you’ll have to dilute yourself. Whatever you choose, follow the directions on the package, and try to treat your mint early in the morning to avoid burning wet leaves in the mid-day sun.
Especially if you have a heavy infestation, you’ll probably need to apply the insecticidal soap multiple times before your mint plants are clear of bugs. You may want to take a look at this brand.
5. Nutrient Deficiencies
In the first section, we talked about water leading to plant starvation: The nutrients were there, but your mint just couldn’t access them.
This is the same starvation problem, but with a twist. In this case, your soil is actually deficient in essential nutrients.
Take a look at which areas of your mint’s leaves are yellowing to get an idea of which nutrients are lacking. Here are the most common ones that cause yellow leaves:
Even though these nutrient deficiencies are the most frequent culprits, there are others that could be to blame for yellow leaves on mint.
For a full list of how nutrient deficiencies affect plants, stop by this article from the University of Missouri. It’s pretty fascinating!
Rescue Plan: Use Fertilizer to Boost Nutrients
If you’re pretty confident you can tell which nutrient your mint is craving, choose a fertilizer that has a high concentration of that ingredient.
Otherwise, if you’re not quite sure which nutrient deficiency might be to blame, an all-purpose formula gives you the best chance of success.
6. Fungal or Viral Plant Diseases
Fungal and viral diseases plague plants of all kinds, and mint is no exception.
Fungal diseases that cause yellow mint leaves are:
- Verticillium wilt
- Mint rust fungus
A viral disease that can strike mint with yellow foliage:
- Cucumber mosaic virus
Let’s look at each of these in more detail.
Verticillium wilt. This fungus starts out as brownish discoloration along the mint leaf perimeter. As the wilt fungus moves inwards, the leaves take on a brittle, curled shape and turn yellow throughout.
Here’s what Verticillium wilt looks like on a blackcurrant bush:
Rescue Plan for Verticillium Wilt: Destroy Affected Plants
There is no treatment for Verticillium wilt, and the fungal spores can infect other plants.
Immediately pull the affected plants out by the roots and dispose of them in the garbage or by burning. Do not throw them on your compost heap or anywhere else on your property. Wash your hands and clothing well after handling diseased plants and use bleach to clean any tools you used.
Monitor your remaining plants closely, and promptly remove any that show signs of infection. Fungal spores can live in the soil for a couple of seasons, so avoid planting your annual mint in the same garden area every year.
Mint rust. Rust fungal infections affect many different species of plants, including roses and tomatoes. However, mint rust is specific to the family of mint plants.
This powdery fungus shows up on the underside of leaves as yellow, orange or brown spots. As the mint rust spreads, it causes leaves to die and drop off. The fungal spots eventually turn black and release spores that fall to the ground or carry on the wind.
This is what rust fungus looks closeup. Notice how the entire leaf underside has a yellow tone:
Rescue Plan for Mint Rust: Better Airflow, Plant Removal, Fungicide
If the infection is in its early stages, try a few changes in your care routine as your first line of defense. Mint rust loves damp conditions with minimal airflow, so make sure to leave at least 18 inches of space between your plants.
You may need to prune or even pull out some plants to achieve good airflow. When watering, always water directly on the soil surface rather than getting your mint leaves wet.
Mint rust can be difficult to clear up, and pulling out the affected plants is another option if you prefer to avoid chemical treatments. Make sure to pull out the entire root system and dispose of all plant matter by burning or in the trash.
Since mint is an edible leaf crop, using harsh fungicides should be your very last resort. However, they are effective. If you choose to go this route, pick a vegetable-safe formula and follow all directions on the package carefully. In particular, make sure to note when it’s safe to harvest your mint leaves again.
Cucumber mosaic virus. It doesn’t happen too often, but mint is susceptible to cucumber mosaic virus infection.
Research shows that insect vectors are key in spreading cucumber mosaic virus, with aphids being a prime culprit. (This is another good reason to nip an aphid problem in the bud!)
Cucumber mosaic virus gets its name from the yellow areas compartmentalized between green veins. Here’s what it looks like on a cucumber leaf:
Rescue Plan for Cucumber Mosaic Virus: Destroy Affected Plants
Unfortunately, there’s no remedy for cucumber mosaic virus, so your real goal here is to prevent it from infecting more plants. Follow the same steps we outlined above for dealing with mint plants infected with Verticillium wilt.
To prevent future loss of your mint crops, keep a close eye out for aphids or other sap-sucking insects. If you spot any, follow the steps we outlined above for using insecticidal soap right away.
Mint is a hardy plant, but it still needs proper care and conditions to flourish and produce a bountiful, flavorful harvest.
Fortunately, in many cases, all it takes are a few tweaks in your care routine to stop your mint leaves turning yellow and start reclaiming the green!
Do you have any other questions about yellowing on mint leaves? Let us know in the comments! And if this post is helpful, don’t forget to share it with your friends on social media!