It was recently announced on the official Pokémon website that there will be an event in Pokémon GO this weekend in which Grass-type Pokémon will be given higher spawn rates. The event lasts from tomorrow (May 5) through May 8. Specific times for when this event starts and stops were not given, but we can probably assume based on the timeframes of recent events, such as the Egg event from last month and the Water Festival event from March, that this new event is likely to start at 1:00PM PST on May 5 and end at 1:00PM PST on May 8. Unlike previous events, it seems this new event will only increase Grass-type Pokémon‘s spawn rates and nothing else, whereas past events have usually included new items or increased the amount of XP or candy players receive.
This event will be a good way to catch rare Grass-type Pokémon such as Bulbasaur and Chikorita, as well as their evolutions. It will also be good for those who need to stock up on Sunkern or Oddish candies so they can finally evolve them using a Sun Stone, one of five evolutionary items added to the game earlier this year. Other Grass-type Pokémon that will have increased spawn rates include Paras, Parasect, Bellsprout, Weepinbell, Victreebel, Exeggcute, Exeggutor, Tangela, Hoppip, Skiploom and Jumpluff. Celebi is also a Grass-type Pokémon, but it is very unlikely that you will come across one during this event since Niantic has yet to include any legendary Pokémon in the game to date.