We cherish too, the Poppy red
That grows on fields where valor led,
It seems to signal to the skies
That blood of heroes never dies.
Some history from usmemorialday.org:
Since the late 50’s on the Thursday before Memorial Day, the 1,200 soldiers of the 3d U.S. Infantry place small American flags at each of the more than 260,000 gravestones at Arlington National Cemetery. They then patrol 24 hours a day during the weekend to ensure that each flag remains standing.