As I understand it now, poppies flourish in disturbed soil. They grow quite well amongst the barbed wire, exploded shells, and the bodies of the soldiers who fell in battle. They are described as giving hope where hope is gone. John McCrae's poem, In Flanders Field, gives an account:
In Flanders fields the poppies blow
We are the Dead. Short days ago
Take up our quarrel with the foe:
The ones we honor are not here to be honored. We can't shake their hands to thank them for their service. We can only remember them and thank their families for their sacrifice.
If you're interested in reading more about Memorial, please go to the Memorial Day website and read for yourself.