Brown mint leaves are a symptom that looks like it would be attributable to 1 problem, but it can actually be due to several reasons (just to be confusing!). What I have learned from growing mint is that the texture and the location of the brown on the leaves tells you what you need to know before you intervene.
This is how to read your mint plant to find out what’s causing it to turn brown.
Touch the Leaf First
Prior to checking the soil, changing up your watering routine or attempting to implement any treatments, I’d recommend that you to touch the brown area first, as this is the biggest diagnostic clue.
Is it crispy and paper-thin on its tips and leaf edge? Low humidity and underwatering are the most likely culprits; the leaf is drying out from the outside inwards.
Is the leaf soft, dark brown and almost translucent in the centre? Then I immediately suspect root rot due to overwatering or poor drainage.
Are there tiny dusty orange or perhaps rust-coloured spots on the underside of the leaves? Then, mint rust is the most likely problem, which is not anything to do with watering and requires a different treatment.
The leaf texture is always the first thing you should check!
The Overwatering Trap
When I first grew mint for mojitos on my kitchen windowsill, I committed the classic mistake, which was to assume mint is hardy enough to tolerate anything and loves moisture, watering it nearly daily. Of course, this was a mistake, and in around 3 weeks, the vibrant green leaves had developed a sickly brown tinge to them, which started from the bottom. When I gently persuaded the plant out of its pot, the roots were not a healthy white but mushy, brown, foul-smelling mush.
Mint likes the soil to be consistently moist, but it despises waterlogged roots, with the soil completely saturated.
To understand exactly how overwatering browning is different from underwatered brown mint leaves, I did a simple test with 2 purnings from the same root-bound plant. With the first cutting, I planted it into soil amended with grit and put it in a small terracotta pot (which is porous and therefore dries out very quickly in the sun. With the second pruning I planted it into a plastic pot without drainage holes and kept the soil constantly damp.
The results were definitive, with underwatered mint turning paper-thin with crispy leaves starting at the tips, whilst the rest of the leaf stayed bright green, whereas the overwatered mint plant turned a pale yellow first and then developed a soft dark brown patch starting from the centre of the leaf going outwards, and it turned translucent where the cell structure had actually collapsed.
The fix for each is the opposite of the other in that for a mint with crispy brown leaves, soak the soil thoroughly and let it drain through the drainage holes in the base. If the leaves are mushy, then stop watering immediately and check the roots. If they are brown and foul-smelling, then the rot may have set in, in which case I’d throw the mint away rather than in the compost heap, as this can spread disease.
My top tips for watering mint so it stays green…
- Always plant in well-draining soil, such as compost with around 10% perlite, grit or sand to help improve drainage. What we are trying to achieve is a soil that allows excess water to drain so that the roots don’t become waterlogged, yet with good-quality compost, it should hold enough moisture so that the roots have enough access to moisture without being saturated.
- Plant mint in ceramic or plastic pots with drainage holes in the base. You can use clay or terracotta pots, but the problem is that they are porous and therefore can heat up and dry out in the sun too quickly. Ceramic and plastic pots are impermeable, which helps to retain the moisture better.
- I usually water my mint every 3 days in a heat wave, or once a week in more settled conditions. You can feel the soil to an inches depth. If it still feels damp, then skip watering until it feels slightly dry, but not bone dry, and your mint is going to thrive.
- Always plant mint in a pot with drainage holes in the base!
The Orange Underside: Mint Rust
This last summer, my big mint plant developed brown spots on the leaves that sort of looked like sunburn, but the brown spots were on the lower, more shaded leaves, which was confusing. So I turned the leaf over and found lots of tiny, dusty orange pustules on the underside.
This is what’s called mint rust, caused by the fungus known as Puccinia menthae, and it’s one of the most often misdiagnosed mint problems, as the upper surface of the leaf looks like regular browning, whereas it’s the orange pustules that are the diagnostic signature that defines mint rust.
Mint rust spreads primarily through humidity and overhead watering, and the spores can overwinter in soil and leaf litter.
The only effective response for mint rust is to trim the entire mint plant back to the soil line and dispose of all affected leaves and stems in the bin rather than compost them, as they can survive a compost heap and always water your mint plants at the base of the plant rather than on the leaves.
The rhizomes underneath the soil line can cause new growth to emerge that is healthy.
The Root-Bound Chokehold
This is the case that I find most online guides tend to miss, and it’s responsible for a lot of the browning that gets blamed on watering.
Mint plants spread through underground runners called rhizomes (which is why I recommend growing mint in a pot and not in a garden bed, as it can spread and be difficult to contain). In the container, the runners hit the walls and circle around the pot over and over again until there is more root than there is soil! At this point, the mint cannot retain moisture or nutrients as it is mostly root mass without soil. The browning foliage that results looks like drought stress because it is essentially drought stress, but overwatering won’t fix it.
The test…If you squeeze the sides of a plastic pot and it feels hard without much give, then it’s likely the root ball has filled it. I would tip the mint out and look to see if you have more roots than soil.
How to fix it…Take a sharp pair of pruners and snip the rootball into quarters; keep the section with the healthiest top growth, repot it into new compost, and either pot up the rest or get rid of it. This feels rather brutal, but you’re giving the mint exactly what it needs, and it thrives on this kind of intervention. Within 2 weeks, you’ll see new growth.
Light: The Slow, Overlooked Cause
Mint plants are often described as shade-tolerant, but there is some nuance to this.
I once moved a pot of mint from a sunny south facing patio in full sun and kept a different one on a windowsill in a north facing room, and the outdoor mint suffered sun scorch with bleached white patches that turned papery brown on the most exposed leaves. For the indoor plant in the shade, the lower leaves turned brown and dropped off as the mint selectively sacrificed the foliage it couldn’t support from the lower light levels.
Both had rowb leaves and neither needed more or less water, and the causes and fixes were very different.
The sweet spot for mint that we should strive for is morning sun followed by afternoon shade, which is enough light to sustain lots of aromatic leaves without the light intensity taht scorches the leaves in the afternoon.
The Quick Diagnostic
| Appearance | Texture | Likely Cause | Fix |
|---|---|---|---|
| Tips and edges are brown | Crispy, paper-thin | Underwatering or low humidity | Deep soak; improve airflow |
| Large soft brown patches | Mushy, translucent | Overwatering or root rot | Stop watering; repot if roots are affected |
| Tiny orange spots underneath | Dusty, powdery | Mint rust | Cut to soil line; water at base only |
| Lower leaves yellowing then browning | Dry, dropping cleanly | Low light or root-bound | Move to brighter spot or divide roots |
| Bleached patches turning brown | Brittle, papery | Sun scorch | Shade from intense afternoon sun |
Mint is turning brown, and not sure which category fits? Describe the texture, location, and whether there’s anything unusual on the underside of the leaves and I’ll help you work it out.