I have a banana tree that was growing fine in pots for about a year and a half. I kept up repotting it, but once it got about 5 feet tall and in a 30 gallon pot I decided to plant it in the yard. Not long thereafter, it started to decline. The leaves weren't very green, it didn't sprout new leaves very fast, and the trunk has become somewhat soft, dark colored, and wet. I suspect some kind of fungal infestation.

Any cures or advice to prevent this from happening again? The neighbor has a 20' tall stand that is constantly producing bananas and I am jealous!