Naomi indicates to Ruth that in spite of Boaz’s delegation of authority in providing for her wellbeing among his watchful stewards and reapers of the harvest, it is he that is doing the actual winnowing of the barley harvest. It is only he that is separating the grain from the chaff.
The barley harvest generally began in April and the wheat harvest extended through mid-June. But please note, even though the winnowing must take place for both, it is the barley that is the focus of attention here.
At any rate, they were introduced to one another, and Boaz was smitten. He decided that he wanted this gal. But Naomi is in the background, and she is pushing the gal. What she said, in effect, was "You have to make your intentions known to this man, so that he knows which way to proceed." That is why Naomi got Ruth to go to where Boaz was lying down. It was during the barley harvest.
