Forum Thread
How do I berry garden
Forum-Index → Help → Answered → How do I berry gardenHere all of your seeds are listed alphabetically, the stars beside them measuring how fast they grew. Screenshot.
To plant a seed, you must click the Seed and select the Level you want. You can pick individual spots or hold shift and click to fill the whole row. Screenshot.
After a while, they should grow though watering them and certain mulches will make them grow faster.
You will get a notification when they're ready to be harvested, which you do by returning to the Berry Garden and selecting the basket.
more information here

As for the answer, the berrygarden is automatically unlocked at level 8. For more information, please click the link that Malkins linked~

Art credit: gelatin