aka "Green Grow the Rashes (or Rushes) O" [Roud 2772; G/D 7:1297; Ballad Index SBoA097; Bodleian Roud 2772] is a Scottish song written by Robert Burns and published as song 77 in the Scots Musical Museum Vol 1 (1787). Burns set the song to a traditional Scottish tune of the same name first published by William MacGibbon in Book 1 of Scots Tunes (1742).
[Chorus] Green grow the rashes, O Green grow the rashes, O The sweetest hours that e'er I spend, Are spent among the lasses, O
NOTE - There is an unrelated Children's Counting Song called "Green Grow the Rashes O" that involves counting in each verse usually from One to Twelve.