Instructions
Obtain the Squirtbottle from the girl inside the pink house in Goldenrod City. Go to Route 36, located south of Ecruteak City.
Walk up to the Sudowood on Route 36 and use the Squirtbottle. When you spray the Sudowoodo, it attacks. Defeat or catch the Sudowoodo. After the fight, a flower shop owner appears.
Take the Berry Pots from the flower shop owner. You also receive six berries to plant or give to your Pokemon.
Open your inventory and scroll to the Key Items tab. Select "Berry Pots." Choose one of the four pots, then select the berry you want to plant there.
Check on the Berry Pots periodically. Tap a pot to add water to it. If you do not water the berry, it will not grow into a plant. When a plant appears, tap it to collect the berries.