The Hakuro Nishiki Willow (
Salix integra 'Hakuro Nishiki') will absolutely LOVE wet feet, and grow twice as fast.
We have one planted next to the big display pond by the front gate at work, and it is literally planted in boggy soil and the edge of the pond where it is designed to overflow during rains. It is also now at least 10' wide and about 7-8' high. (been in the ground about 3 years, since the summer before my boss died)
The banana will love soil that stays consistently moist...but not soaking wet.
I know some people have grown bananas in the pond, and some varieties may like water more than others (like Elephant Ears) so I will not support a blanket statement declaring all bananas tolerant of wet soil.
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I think it would be best to plant it on a bit of a slope (which you have a lot of!) and keep it well watered.
Maybe where you can backwash pond water for it.
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