Plough Monday is generally the first Monday after Epiphany, 6 January.

Wikipedia : Plough Monday    https://en.wikipedia.org/wiki/Plough_Monday

PLOUGH MONDAY SONG   https://www.youtube.com/watch?v=y0m5twlZ4sI
MUDCAT:Plough Monday - you couldn't make it up    /mudcat.org/thread.cfm?threadid=107925&messages=26#2241513

Link to COME SEE THE BOYS GO ROUND posted below by Felipa