Yeats used the phrase "Salley Gardens" to evoke a sense of Irish folk tradition and romanticism. "Salley" is an archaic word for "willow," and "gardens" could refer to a meadow or any peaceful, verdant setting.
So, while the Sally Gardens are not a real place, they exist as a powerful image in Yeats' poetry, representing a place of beauty, love, and bittersweet longing.