A poetry question

In James Taylor's song, "Gaia," he uses a phrase that I thought he had borrowed from Keats, but now I can't find any attribution other than to Mr. Taylor. The full song's lyrics are here.

Here's the story. A few years ago I assembled photographs on snapfish.com to have calendars made up, and went in search of quotations to use as captions. I found "the petal sky and the rosy dawn," a quote that I recall as having been attributed to Keats, and used it as a caption for one of my [many] sky pictures. This morning I thought to go looking for the rest of the poem and I can find no "petal sky/rosy dawn" other than in "Gaia."

I'm sure that there is some one among the readers and writers here who can help me with this Sunday morning wonder question.