Instructions
Fight the Sudowoodo on Route 36 north of Goldenrod City and a man will show up and give you the Berry Pots key item and some berry seeds.
Assign the Berry Pots to the bottom screen of your DS so you can keep an eye on them.
Go to the Flower Shop in Goldenrod City, in the center of the Johto region, and talk to the girl inside to get the Watering Can.
Buy some Growth Mulch from the Flower Shop -- this will make your berries grow 75 percent faster.
Plant the berry seeds in the Berry Pots, use the Growth Mulch on them, and water them using the Watering Can.
When you see the berries have fully grown on the bottom screen of the DS, select the Berry Pots to harvest them.