How do you know when a poem is finished?
I tend not to. I am an editor by trade and by instinct. Learning when to let a poem go is an ongoing struggle for me. I don’t believe a poem is ever finished, really. Not only may it eventually be adapted by the author again, it will certainly be adapted, in how it is seen and heard and interpreted, by every person who eventually reads or hears it.
Honestly, I don’t think any art is static as long as there is a person who may still stumble across it and bring it back to life by engaging with it.