Mark Van Doren:
(Hope, Vermilion County, Illinois, 13 June 1894 – Torrington, Connecticut, 10 December 1972).
American poet, literature professor and critic.
He was awarded the Pulitzer Prize for poetry in 1940.

June in the branches sleeps its fill, July and August are dead still.

The couplet captures the particular quality of midsummer stillness in nature, painting a progression across the summer months. June is still active — full of growth, birdsong, and the busy energy of early summer, but a drowsiness is already settling in (“sleeps its fill”). July and August then deepen that drowsiness into something close to suspended animation — “dead still.” The air grows heavy, the woods go hushed, wind drops, and the world seems to hold its breath under the oppressive heat. It’s not a threatening stillness, but a languid, contented one, like a creature that has eaten well and settled in to sleep.
Origin:
The lines come from the poem “Hardhead,” published in “Spring Thunder and Other Poems” (1924). The phrase has since been widely quoted in collections of seasonal poetry and nature writing, which may give it the feel of a traditional saying — but it has a single, identifiable literary origin.
Author: Mark Van Doren (1894–1972), the Pulitzer Prize-winning American poet, critic, and Columbia University professor.