When you are writing an essay about a poem and you are quoting the poem itself, you should cite the poet because he is the author/owner of the words you are quoting. When you go to create you works cited page (if using MLA style, which is the standard for English papers) you will cite the poet, the poem's title, the book title where you found the poem, the writer/editor of that book, and any other publication information required. If you look at the MLA link below you will see samples of what information the works cited entry requires. To make all of this clear in the body of your essay, it is easier to work the poet and title into the text of your own writing.
If you are quoting or paraphrasing an author's idea about the poem, then you need to do a traditional internal citation, which includes the author's last name and the page number in parentheses at the of the section that includes those ideas. It is especially important to give credit with citation ANY ideas that were not your own.