The Mary alluded to in the traditional English nursery rhyme is meant to be Mary Tudor, or Bloody Mary, who was the daughter of King Henry VIII. Queen Mary was a staunch Catholic and the garden referred to is an allusion to graveyards which were increasing in size with those who dared to continue to adhere to the Protestant faith - Protestant martyrs.
This is a nonsense song - I've got no idea what its about. It refers obliquely to some of the awful part time jobs I've done to keep things going I suppose.
