The Grass so little has to do
I wish I were a Hay
The speaker has spent the poem cataloging the idle, privileged lifestyle of a woman who is so beautiful and wealthy she makes a duchess look common. In these final lines, the speaker unequivocally rejects that life, choosing hay over grass. In addition to being a food source for beasts of burden, hay is also used as to insulate buildings. It may not be pretty, the speaker implies, but at least it’s useful. 
 Like Stanza 2 with the pearls/duchess, Dickinson introduces an object first (a barn) and waits a few lines to mention something that puts it in context (hay).
The Grass