Excerpt from General Orders No.11, Washington, D.C., May 5, 1868:
The 30th day of May, 1868, is designated for the purpose of strewing with flowers or otherwise decorating the graves of comrades who died in defense of their country during the late rebellion, and whose bodies now lie in almost every city, village, and hamlet church-yard in the land. In this observance no form of ceremony is prescribed, but posts and comrades will in their own way arrange such fitting services and testimonials of respect as circumstances may permit.
I got that excerpt from a better Memorial Day article than I have ever written or ever hope to write.