The first question I'd ask a poet who asked me this question of show/tell:
What is the subject of the poem?
Then I say:
Instead of show/tell, I prefer the continuum of heavy detail and minimal detail. Detail about events, actions, emotional states, whatever.
Still I'd like to answer the OP:
"Telling" (so frowned upon these days) is the barest level of necessary detail that still permits basic comprehension of a text.
"Showing" always builds up/out from "telling"
A professor and I once spoke of 'narrative doors' (I'm repurposing and paraphrasing both) - Imagine you're walking in a vast hallway. The eventual goal is to make it to the other side of the hallway. There are doors in the hallway. Closed. Do I rush through the hallway? Or do I open the doors and explore what is behind them?
I must add: Poetry, taking a billion forms, might be just one broken line and still be an effective communication.
So if above I asked: what is the subject of the poem, I might now ask: what is the goal or objective of the poem? What is the purpose of its expression ?