Niantic have announced the details for the 20th Pokémon GO Community Day which takes place on September 15th, 2019 at 11:00 AM until 2:00 PM EST. The featured Pokémon for this day is Turtwig. Turtwig will appear in the wild more frequently for three hours that day. If you evolve Grotle into Torterra, your Torterra will know the move Frenzy Plant. The 3x Catch Stardust and 3-hour Lures bonuses will also be available that day.

Source: https://pokemongolive.com/events/community-day/