You may be overwatering it with the leaves turning yellow.. most herbs like a dry pot.. not bone dry, but not wet..also if it's getting leggy, cut it back..first I would test that soil and if its too wet, repot the spearmint. It won't be long and you can place it outside if you can get it to hang on.

Poor thing is being squashed to death. The roots probably are so pot-bound that it can't access either food or water. It needs repotting.

Thanks to both of you.

daisyduckworth, I have the plant in a big-sized pot, quite a bit bigger than than the plant itself.

How much bigger than the plant should the pot be? Or are you suggesting that I just throw out the current soil and repot in the same pot with new soil? Please do clarify.

Thanks,

charlie

With mint, it's difficult to say what is a big pot and what isn't! You could have a pot the same size as your Olympic swimming pool, and eventually the mint would outgrow it! Most people's idea of a large pot might be something like one 30cm in diameter - for mint, that's a very small pot indeed.

The thing to do is to upend the pot from time to time to expose the roots. If they're going round and round and there's not much soil, then it's well and truly time to repot - either into a much larger pot, or divide the plant and repot into the original, with a small section of the plant.

With mint, and many other plants as well, it's not the bits you see that are important, it's the bits you don't see - the dirty bits underground! Mint has a very aggressive root system which can far exceed the leafy bits at the top.

My rule of thumb is: if your potted mint isn't doing so well, it needs a much larger home!