Hello. I've got a question about my banana plant. It's nice and green and appears to be growing everyday. My concern is the leaves. The oldest or outer most leaves are falling down. I'm talking about the whole leaf and the part of the stem(?) it's attached to falling down to the ground and causing a fold at the base of the stem near the ground. I've been looking at pictures online and I'm not seeing pics of other banana plants doing this. The leaves are still greenish and the stem part is still green. Any ideas what I'm doing wrong? What I can do to stop it? Is it normal?

Thanks