I think it may be some kind of mineral defiency. It looks as though you have it in a pot - have you fed it at all? Also is the plant well drained, yet kept moist all the time?

While mint is a survivor, I suspect that the tropics are probably outside of mint's normal comfort zone with regards to heat. Do you have your plants in a place where they get morning sun but not the hot rays of afternoon? If so, you can probably 1.) make them happier to not be baked but 2.) better manage the moisture level. If you can better manage the moisture you won't be watering all the time which has probably leached minerals from the potted plants' soil.

FataMorgana

Hi there,

Thanks for your insightful answers.

Yes, the tropics can be quite hot for some Mediterranean herbs but I have good success with most of them by growing them in an area where they will only get morning sun.

Do you think my mints may be suffering from any viral or fungal disease?

sghort - mint (Mentha spicata) is not actually a Mediterranean plant. It is at home in cool climates like the British Isles, parts of Europe and Western Asia. Its natural habitat is cool and moist so it is definitely pushing it to grow it in the tropics as FataMorgana says.

Hi All,

flora_uk - I am aware that most mints are not exactly Mediterranean. What I wanted to say was that in the tropics here, we have been quite successful with the growing of some of these herbs here with the use of an appropriate soil mix and a coolish location.

Here in the subtropics of Australia, my mints do very well indeed. Of course, I keep them in pots, and they need repotting at least twice a year because of their aggressive root systems.

I find that if they are kept in all-day full sun, the leaves are smaller but much more flavourful; in partial shade the leaves are larger, but less flavourful. Certainly, they don't like having the soil dry out at all, so the water must be kept up to them at all times. Remember, in pots, the nutrients will leach out fairly quickly for such an aggressive-growing plant.

Mine are in the sunniest spot in the garden, sitting on concrete pavers, so mints can certainly handle the heat!!

I can't access your photos, but I would suggest that your plants probably need repotting. They'll need good-sized pots, too. As the roots fill the pot, they'll be unable to access water and nutrients so easily, and therefore will not be as healthy as they should be - they choke themselves to death.

It's funny the different results different people can see. I grow my mints directly in the ground. But they resent the hottest areas of my garden - of course I am not watering them daily as you would a potted plant. I live far from the Tropics. In an average summer here, I get less than a dozen days at 90+ degrees Fahrenheit and winter is snowy and cold where it can get below 0 degrees Fahrenheit.

Getting plants locally sometimes will offer you plants that are more tolerant to your local conditions.

FataMorgana

We get similar symptoms when our mint is attacked by leafhoppers. Often, by the time you get a good look at the tip, they will have hopped away!

Kevin : )