“When Lilacs Last in the Dooryard Bloom’d” represents Whitman’s expansive free verse style, seen in poems like “Song of Myself” before and “Out of the Cradle, Endlessly Rocking” later. Whitman’s extended lines demonstrate his effort to create a kind of prosody appropriate for America: its complex, busy cities, its open prairies, and its rugged western terrain. Whitman made the Romantic ideal of voicing the common man into a literal reality, rather than a poetic stance. Rather than organizing his poems with meter and rhyme, he employs rhythm and repetition, echoed syllables, and percussive alliteration. The number of syllables per line in “Lilacs” ranges from six to over 20; syllabic stresses can be hard to determine, since line length remains in flux throughout the poem. Even within cantos, the line lengths can widely vary.

For instance, in Canto 12, Whitman portrays the various geometry and geography of the country, contrasting “Manhattan with spires” (Canto 12, Line 2) against the “far-spreading prairies” (Canto 12, Line 4) in one long periodic sentence.