What is the green rain event in Stardew Valley?

Green Rain is a rare summer-only weather event (added in the 1.6 update) that can occur once each Summer and fills the valley with a translucent green rainfall and visual tint. During the day the event spawns large amounts of mossy growth, temporary Green Rain Trees, and fiddlehead-fern stalks across most outdoor areas, giving players a one-day chance to harvest moss, mossy seeds, fiber and fiddlehead ferns; it’s harmless to the player and crops. See the community Weather guide for details. Stardew Valley Wiki - Weather

For practical impact and tips: the event is typically hinted by an “anomalous reading” on the TV weather report the day before, and many NPCs shelter in the Stardrop Saloon during the green rain — making it easy to find villagers if you need to raise friendship. Common effects include: - Large spawn of weeds and moss-covered trees (not on the Beach or Calico Desert). - Chance to get mossy seeds, fiddlehead ferns, and extra fiber from chopping or shaking trees. - No damage to the player or livestock, and it does not water crops.

If you see the forecast, use the day to farm moss-related materials and visit common gathering spots; for a practical how-to and examples, see this guide. GamesRadar: green rain explained