Niantic has announced that to celebrate the equinox, players of Pokémon GO will have a chance to get some Grass-type Pokémon like Oddish, Exeggcute, Sunkern and Shroomish more easily from March 19th, 2019 until March 26th, 2019.

Celebrate the equinox with Pokémon GO!

Trainers, With spring days arriving in the northern hemisphere and autumn quickly approaching in the southern hemisphere, it’s the perfect time to celebrate the coming equinox with some Grass-type Pokémon.

Date + Time Mar. 19, 2019, at 1:00 p.m. PDT to Mar. 26, 2019, at 1:00 p.m. PDT (GMT −7)

Features Grass-type Pokémon—like Oddish, Exeggcute, Sunkern, and Shroomish—will appear more frequently in the wild. Lunatone and Solrock will switch hemispheres at the start of the event in celebration of the equinox! These Pokémon will stay in their new hemispheres after the event.

Raids

• Grass-type Pokémon will be available to challenge in raids.

Field Research

• Limited-time Grass-type Pokémon Field Research will be available during this event.

Move
New moves will be permanently added to the game.

• Acid Spray: Arbok, Victreebel, Tentacruel, Muk, Alolan Muk, Quagsire, Qwilfish, Octillery, and Swalot.
• Leaf Tornado: Victreebel, and Shiftry.

New seasons mean new adventures, Trainers! Let’s get out and GO!

Source: https://pokemongolive.com/post/equinox2019