One thing about heading out to the Skagit Valley tulip fields at sunrise is that I shared the fields with the agricultural workers. They weren't picking the fields clean though. They would walk down a row and carefully select flowers for bouquets. However I did see several fields picked clean like this, and wish I could relay the reason for it. I do know that these farms dig up and replant these bulbs each year. Maybe clearing the flowers at once helps speed the bulbs to their resting phase?