Country Gardens is a Morris dance tune - that is why Percy Grainger teamed it with Shepherds Hey, also a Morris Tune. I think Grainger recorded a piano roll called Morris Medley.
Grainger, I think, got his tunes from the FieldTown Morris versions of the tunes, which also occur in other Morris traditions. The Longborough dancers also call a variant of the tune Highland Mary - though I do not have a clue why, it is called Country Gardens elsewhere. I am sure that the lyrics are fairly recent - they have a sick ring of English 19th century sentimentality.