Gabe15

What appears to be happening is that there is a salt buildup in the soil. Tell me if I'm wrong, but I'm guessing it is a 'Super Dwarf Cavendish' that you have been feeding with miracle-gro or something similar with for awhile. These types of fertilizers are easily over-applied and accumulate in the soil where they can lead to problems like what you are seeing, usually shortened leaves which bunch up and to not come out fully or properly. Even if you were not using a chemical fertilizer, any type of fertilizer (even organic) can build up in the soil if over-applied and lead to the same problem. The 'Super Dwarf Cavendish' is especially sensitive to this and other environmental stresses which it often responds to by dieing back and suckering. There's not a whole lot you can do right now, the plant won't die, but it will probably continue to grow smaller and smaller leaves, and may actually decrease in height and shrink as it grows (essentially growing shorter...a few strange phenomenon). Each leaf will be smaller and come out a little lower, pushing the other older ones down until it effectively shrinks the whole plant.

If you have been fertilizing with anything, don't add any more, but continue to water until the spring when you can take it outside and thoroughly wash/drain the soil.

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Growing bananas in Colorado, Washington, Hawaii since 2004. Commercial banana farmer, 200+ varieties.