Mint has a reputation for being the hardest herb in the garden, and on some occasions, you can’t stop it growing even if you wanted to!
However, for some of us, the experience can be very different, with the mint wilting, yellowing, turning brown, and suddenly dying despite our best efforts.
I have grown mint for many years (Moroccan, spearmint, peppermint, chocolate mint), and a few of these have died before I understood what I was doing wrong.
Interestingly enough, I have found that one of the most common causes is completely counterintuitive.
This guide tells you, from my experience, how to diagnose your mint and how to save it.
The Root Bound Paradox: When Mint Is Too Successful for Its Own Good
From my experience, this is one of the most common causes of dying mint, and most articles actually miss it!
One spring, my container of Moroccan mint that had been thriving for more than 2 years started drooping and yellowing despite daily watering. I assumed it was struggling, so I investigated. I gently slid it out of its pot, and there was almost no soil left! It actually looked rather fascinating and puzzling, and I remember potting it up with my favourite blend of compost.
The roots had formed a solid, woody, almost brick-like, entangled mass that had turned hydrophobic (caused water to run off the surface rather than infiltrate and reach the roots). All the water had been running down the side of the pot and through the drainage holes in the base, and the centre of the spectacular root entanglement was dry!
The great irony being, of course, the mint I was watering very often was dying of thirst.
Here’s the botanical explanation for this…Mint plants are aggressive spreaders that send out underground stems or runners called stolons. These horizontal stems that grow outward produce new mint plants, which is why the advice is not to plant them in a bed, as they would take over.
However, in a container, these stolons have nowhere to go, so they just keep circling the pot and compact and even displace the soil until the root mass becomes so dense that water does not infiltrate, hence the drooping, yellowing leaves.
Here’s the fix…we need to be hard and not gentle here! A dramatic intervention is required. Remove your mint from the pot and take a saw or even a sharp spade and slice the rootball into quarters. Keep one section healthy and prune the roots back in proportion to the plant (don’t be shy here, mint is tough) and repot the mint in good compost (multipurpose compost is fine, but 10% worm castings and 10% perlite works best in my experience).
I know this feels dramatic, but just do it! Mint is highly resilient to this level of disruption, and a mint with most compost is going to be much happier, within weeks new growth emerges with aromatic leaves.
How do you prevent this? I’ve found the best way is to repot my mint every spring, regardless of whether it looks like it needs it to get in front of the problem!
Diagnosing the Problem: Drunk or Thirsty?
Before we talk about the solution, we need to identify the correct cause. Surprisingly and confusingly enough, overwatered and underwatered mint can look the same from above, with both having yellow, wilting leaves, and if you get the diagnosis wrong and apply the wrong fix, the problem gets worse.
Here’s how I tell them apart…
Wilting, crispy leaves dropping off from the bottom up or drooping, and the pot feels light and pulls away from the pot edge. This is indicative of severe dehydration, which is often combined with the hydrophobic problem as I described above.
Sometimes the sun bakes the soil hard, and the water just runs off the surface without soaking in properly. Hence, the pot feels lighter than you’d expect.
The fix is to water your pot from the bottom rather than from the top. What I do in this scenario is place my mint pot in a basin of water (or if I am outside, a wheelbarrow of water) and let the soil draw up the water through the drainage holes so that the soil is fully hydrated (usually takes 20 to 30 minutes). Afterwards, you’ll feel the pot is much heavier, which is the reassuring sign that you should always look for after watering.
Yellowing, mushy leaf texture with drooping stems, and the soil is very damp… This is always indicative of overwatering or poor drainage and root rot.
Here’s an unusual diagnostic trick…sniff the drainage holes in the base…does it smell sour? Like something has gone off in the fridge? This is root rot bacteria. H
This is much trickier to revive and has a lower success rate, to be honest…However, you can unpot the mint and trim away any black mush roots with a clean pair of pruners (sterilize the pruners between each snip with disinfectant to prevent the spread of fungal pathogens and bacteria ) and dust the remaining healthy roots with some cinnamon before repotting, as cinnamon is a natural anti-fungal that slows any fungal growth on cut root surfaces and improves recovery rates. Repot the mint in new soil, preferably with some added perlite for drainage and give it a good soak to mitigate the shock.
Other causes of too much moisture around the root ball are pots without drainage or saucers underneath pots that retain water and keep the soil boggy. Make sure all your mint pots have drainage holes in the base and drain any excess water that sits in saucers underneath the pots.
The Scorched Earth Reset
This is the most dramatic yet successful intervention of them all! Snipping a plant all the way back nearly to soil level when it’s dying is slightly counterintuitive, but it works…
My friend handed me a poorly looking spearmint plant that she’d been growing in a dark kitchen corner. It had about 3 weak stems and was stretching for light, and also covered in spider mites…
Instinct tells you to be gentle, but there are time where you need to be rough…
I took my pruners and snipped the entire thing down to half an inch above the soil line.
I, of course, kept it watered and moved it to a sunnier spot and with 12 days (during the growing season), some dense new growth emerged gloriously and defiantly!
Here’s a botanical explanation for this…Our mint plants store energy in their rhizomes. These are the underground stems from which the roots and overground shoots emerge. When the top growth of your mint is compromised by pests, disease or even dehydration and poor sunlight, it’s a waste of energy trying to rehabilitate this growth and much better to allow new growth, which has much tastier leaves.
The reason you can do this with mint plants and not other herbs is that mint is perennial and comes back every year, thanks to its established roots, whereas herbs such as basil are annuals and their roots don’t have the same energy reserves to grow new leaves again if they are pruned back to the soil line.
When to use the snip back method:
- Severe spider mites and aphid infestations.
- Powdery mildew or any other fungal disease on the leaves.
- Woody, leggy growth from prolonged low light
- The plant has collapsed, but the roots still smell clean and earthy
One caveat we need to consider…this method only works if the root system is still viable in the pot. If the roots are rotted, then there are no energy reserves to draw on, so always check the roots before cutting back.
Another fungal problem, Mint Rust
This one can catch a lot of experienced gardeners off guard.
Mint rust is caused by the fungus Puccinia menthae, which has bright orange, powdery pustules on the underside of the leaves, often with corresponding yellow spots on the leaf surface. It spreads very quickly in humid conditions.
Whatever you do, do not compost infected cuttings... The spores of the fungus Puccinia menthae are very resilient and even overwinter in a compost heap, and can reinfect your next season’s plants. I recommend all infected stems go in the household waste bin, rather than the compost.
The fix is another dramatic intervention. There is currently no effective treatment for mint rust, so we need to prune the mint back to the ground and dispose of all infected leaves in your household waste and top dress the soil with a thick layer of compost to bury any spores on the soil’s surface. There is no effective topical treatment that will clear a well-established mint rust infection.
The rhizomes push out new growth that starts rust-free. If your mint repeatedly gets rust in the same container, then replace the container (or wash it in disinfectant), and the soil and your mint should be rust-free.
Light and Position of mint…
I have found that mint needs more light than most guides suggest, and the aroma and flavour in the leaves tend to be stronger.
A dark kitchen corner or a north facing window isn’t going to quickly bring its demise, but the decline is gradual.
Instead, what happens is mint slowly etiolates with its stems being long and weak, and the leaves are smaller, which causes it to become more vulnerable to pests and disease.
Minimum: If you are in a northern latitude, I’d recommend full sun, but in a hotter climate, then morning sun with afternoon shade tends to be best (otherwise it can dry out too quickly). When grown indoors on a windowsill, I find it grows best in full sunlight.
If your mint has been in a low-light position and is looking weak, combine a move to better light with a hard cut-back, as the two interventions combined produce faster recovery than either alone.
The One Thing Worth Remembering
Most dying mint plants are not beyond saving as they’re just rootbound, waterlogged, infested, or starved of light, and the fixes are almost always more aggressive than feels comfortable compared to most plants, such as slice the root ball apart, snipping it to the ground, or ditching the infected material entirely.
Mint’s survival instinct is incredible, and we as gardeners just need you to stop being gentle with it.
Has your mint come back from the brink? Or are you currently troubleshooting a struggling plant? Drop a comment below, I’d love to hear what worked.