The setting of "Blackberry-Picking" is mostly outdoors, in a pretty rural place. The boys move from blackberry patch to blackberry patch, trekking through cornfields, briars, and hayfields. They start early and pick all day. It's summer – late August, to be exact – and it seems as though the poem could span a few days. The byre, or cowshed, has its cameo appearance too. It's where the berries are stored.
It seems the poem takes place long ago, so now it's a place in the speaker's memory, though that doesn't take away from the vividness of the scenery. We're given all sorts of colors, smells, and tastes. So even if it happened long ago, it's still crystal clear.