Instructions
Fly to Goldenrod City and walk to the flower shop in the northeast section of the city.
Talk to the girl behind the counter to purchase Growth Mulch. You will need $200 to purchase this item. One package of Growth Mulch is good for only one berry tree.
Walk up to any of the berry trees you have planted and press the action button to apply the Growth Mulch.
Water the plant as needed while it grows. To water the plant, stand next to the tree and press the action button to use your pail. Continue to water the plant whenever the soil becomes dry.
Harvest the berries when the tree is fully grown. The growth time for a berry tree varies depending on the type of berry, so check back frequently.