How do you know when a poem is finished? Do you have a social group or writers group that you work ideas and poems with?
I don't believe that a poem is ever finished. Instead, I would say that while a poem might appear to be complete at a certain point in time, given some distance, there is always room for change.
On average, I typically do at least seven different "final" drafts of a poem before I'd even consider it done. I sometimes will share it with friends and family because I enjoy hearing their interpretation. Often, their take on what I've written isn't necessarily what I intended. That subjectivity though is a fundamental part of the beauty and pleasure of poetry.