The most recent suggestion from guest was proposed earlier on in this thread and refuted with the information that the bent and broom chorus was only added to the Cruel Sister (borrowed from another song) in the 1960s.

re Jim Carroll's 2016 contribution, I understand "May" to refer to the Hawthorn, which also flowers in May. I suppose the names may vary from place to place. I've also heard in Derry (N Ireland) of people warding of evil spirits by placing branches over their doors on May day; the people who told me remembered the custom but it had pretty much died out by the 1970s, when I heard of it. The February tradition of making and displaying St Brigid's crosses does continue.