In the 1819 ballad "La Belle Dame sans Merci" (the beautiful lady without mercy), John Keats does not say explicitly what season it is set. However, there are several lines that provide clear clues. The last two lines of the second stanza refer to a squirrel's full granary and a completed harvest. This indicates that this poem is set during autumn.
The season of autumn does have some significance. When Keats wrote this ballad, he was very preoccupied with death. He was ill with tuberculosis, the same disease that had killed his brother years before. Autumn is the final season before plants die for the winter. To Romantic poets like Keats, autumn represents the time in one's life when they can look back on what they "harvested" as they prepare for life's final stages. In this poem, the knight, who may very well be a representation of Keats himself, faces both love and death. With the harvest over, it is easy to imagine a scene in which plants are beginning to shrivel, and the songbirds have all gone away. The knight finds himself alone in this gloomy landscape. This paints a somber and contemplative mood for the poem. Therefore, autumn is a fitting season in which to set this ballad.