Can you guess which season this poem is set in? "To Autumn" gives us all the ripe, growing things we would expect from a poem with this title, and Keats even throws in an aimless, super-chilled-out lady, to boot.
When you look closely at the poem's images, you notice all kinds of hidden movement. In the first stanza, you get a sense of the "conspiratorial" tone between the sun and autumn, as the unassuming vines and fruits creep around houses and trees until – boom! – everything bursts into a surge of ripeness. The setting of the first stanza is characterized by growth and swelling under the influence of the sunlight, and this growth even carries us into the spring and summer, as if time itself were expanding.
The second stanza is all about the harvesting process. Autumn sits with her "store" of grains like King Midas with his gold. She may have been hanging around the poppy plants too much, because she seems a little tipsy. She just kind of wanders around, inspecting things and taking occasional naps. What a life. Despite being a tad out-of-it, she's a tough bird to track. The speaker follows her around like a bodyguard, from field to brook to, um, cider factory.
In the last paragraph, Keats ties everything together with the idea of music and songs. He uses a few powerful images to suggest that all of nature works in harmony to produce the beauties of autumn. This music is associated with the sunset, in particular, and you might think that the sun has been slowly going down through the entire poem. Only we were too busy admiring the poetic landscape to notice the passage of time, just as the speaker is too busy admiring autumn to notice the approach of winter.