I can only grow things in containers as I have no garden and have an active herb garden mostly consisting of some very happy chives and some potted Bay, rosemary and basil.However the window box I plant my mint in seems to be a dead loss. Sometimes I discover it is too wet and I have been over watering (so it dies) or I find it is too dry (so it dies). I tend to water most plants about the same time and about the same rate but the mint seems to like to fluctuate massively. What can I do to increase the life and survival of my mint?
I'm afraid it won't do well in a trough or window box however you water it. Mint likes a deep root run, so does much better in deep pots than it will in shallow containers, but even then, it inevitably stops growing well after a couple of years. Try getting a pot 18 inches deep and as wide as possible - that way, the mint will be more productive for longer.