I've had a number of problems with potted bananas over the years that I had long believed was mainly a fungus / bacterial problem, but have since come to realize is primarily a problem of underfeeding (particularly potassium). I dismissed the browning of the leaf edges and their eventual loss as normal leaf loss and/or attributed it to the periodic spider mite problems that are always a pain for indoor growers. The plants would get up to an impressive size, but then a foul-smelling rot would set in in the stalks, the stalk would die and the plant would have to start over from a pup. I've lost three very large bananas that way :Þ Potting up always seemed to improve things... for a time. But of course that repotting gave them fresh soil and made the job of them incorporating the nutrients in the soil easier, as they had more root space.
What clicked was when treating a particularly problematic banana (which experienced trouble even at a small size), and I finally ID'ed the soil as potassium deficient... and then in cross-referencing the deficiency found an article talking about bacterial stem rot on a particular plantation (the symptoms of which exactly matched my description) that had been traced back to severe potassium deficiency leaving the plant vulnerable.
Live and learn.
Seeing KH's success makes me want to see if I can replicate it with a properly fed banana. It'd be nice to be able to give the rain barrels to something else (hmm, the question is, what deserves them most...? Maybe an annona?
) At least spider mites shouldn't bother me any more. I recently found a local (and affordable!) supplier of predatory mites/insects that I didn't know existed