Note from "The Illustrated Book of Scottish Songs" (1854):
"Jane Elliot, about the year 1750. 'The Flowers of the Forest' are the young men of the districts of Selkirkshire and Peebleshire, anciently known as 'The Forest'. The song is founded by the authoress upon an older composition of the same name, deploring the loss of the Scotch at Flodden Field, and of which all has been lost except two or three lines."
The air is played sometimes at funerals, but never, of course, at weddings.