Mulberry fields (idiom)

Mulberry fields is an idiom meaning a place where something is happening which produces a lot of activity. It comes from a story in which a farmer had a field full of mulberry trees, and there were so many people picking the mulberries that it looked like the field was alive and buzzing with activity. So, now when we say "mulberry fields" we mean any place where there's a lot of activity and work going on.