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 of the leaves turning brown and was worried.
Your mint leaves may be turning brow because they have received too much water. They may also turn brown if infested with pests like aphids, cutworms, or thrips that suck the sap from them. It could also happen if the plant has outgrown its container.
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.
Over Watering/Poor Drainage
If the majority of the leaves look healthy, but the inner or bottom ones are rotting and turning brown, there’s a good chance that the plant is getting too much water.
This can be due to overwatering, of course, but also by lack of drainage.
Be sure to plant mint in a pot with sufficient drainage and check its roots regularly to make sure it’s not getting too big for its pot.
If the plant hasn’t overgrown its pot, try watering less frequently or watering with a smaller amount. Mint does best in soil that’s moist but not completely drenched.
As mentioned above, it’s possible to overwater mint. However, they do prefer moist soil. If your mint is brittle, with stems and leaves that are turning brown, it needs more water.
It’s best to water mint when the soil has turned dry. You can stick your finger 1-2 inches in the soil to check for moisture. If the tip of the finger is dry, it’s time to water.
Make sure to 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.
Too Much Sun
If the tips of the leaves are turning brown, there’s a good chance your mint is getting too much sun.
The mint plant will prefer full sun for best growth but it also does not like too much heat as it’s a cold-season plant.
If the temperature gets too hot in the afternoon, you may need to cover the plant. If you’re growing the mint in a pot, you can just move it in a shaded location.
Two types of fungi just love mint plants:
- 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.
Prevent mint rust by watering the soil rather than the plant, and thinning the mint to allow for better air circulation. If the mint is potted, water from the bottom.
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.
Pests that attack your mint can cause all kinds of health problems for the plant, in addition to brown spots on leaves. Pests that commonly attack mint are:
A small, soft-bodied insect that is commonly found on the underside of leaves on many plants. They can be varying 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. Make sure to 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 making sure to check 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 be able to spot the small insect under a magnifying glass. Adult thrips are pale yellow or light brown while their offspring are lighter in color.
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, make sure to 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.
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 are able to cure your mint plant and restore the natural green color.
You also need to make sure that your mint leaves are not turning brown due to 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 and 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 of time for future use.
Is it Safe to Eat Spotted Mint Leaves?
If the spots are due to 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 due to a fungus or disease, the leaves are not safe to eat, and the plant needs to be cured before consumption.
Final Thoughts on Keeping Mint Healthy
You should follow the general maintenance of your mint plant to prevent the leaves from turning brown. Because mint is a rapidly growing plant, you need to regularly prune and trim to keep it healthy and in check.
You should use slow-releasing fertilizer in the Spring and throughout the growing season to properly supply it with nutrients and pinch the flowers that form to conserve leaf flavor and prevent color change.