Is an MLA citation needed for a broad description of a poem's theme? I'm trying to figure out whether I need to cite these poems or not.


  “Out, Out—” has its morbid description of a young boy bleeding out and
  its underlying theme of death. “Nothing Gold Can Stay” has its
  pessimistic theme that nothing beautiful can stay beautiful.


I speak so generally that I


Have no idea if it's ethical or not to exclude citation
What I would cite were I to. Generally you cite poems by line numbers. If one were to cite a poem based on a description of its theme, doesn't that encompass the entire poem? This has more to do with the in-text citation part.


Thanks for any help
In general, it's always a good idea to cite your sources. This can especially be the case with older poetry, where there are often differences in spelling, punctuation, and layout between different editions of the same poem. 

So, at the first mention of a literary work, whether it's a direct quotation or an indirect reference, it's probably a good idea to cite the specific version of the poem you're writing about. This will make life easier for everybody involved. You would cite the overall poem, usually as a publication in a larger source, and follow the specific guidelines of whatever style manual the publication you are writing for (or the school you are attending) is using.

For example: 


  Poetovsky, R. "Sonnet 100" in Every Sonnet Ever Written by Anybody, ed. John Smith. Random Publisher, Some City (2000).


Then, if you go on to cite the poem again, you can refer to the specific lines as needed; general statements probably wouldn't need to be cited.