"Now is the month of maying" is one of the most famous of the English balletts (a light dancelike part song similar to a madrigal, frequently with a 'fa-la-la' chorus).
It is based on the canzonet So ben mi ch'a bon tempo used by Orazio Vecchi in his 1590 Selva di varia ricreatione.
For example, a "barley-break" would have suggested outdoor sexual activity (rather like we might say a "roll in the hay").
[3] The ballett forms a key part of Oxford's May Morning celebrations, where the choir of Magdalen College sing the verses from the roof of the college's Great Tower.
It was also heard in 1964 on The Andy Griffith Show episode "The Song Festers".