Instructions
Visit the village and go to Costalot's General Store. There, you can buy all the gardening supplies you need. Purchase several seeds. Carrots and turnips are good starting plants, and both only cost 2 gold coins.
Return to your garden and plant the seeds. Water them until they grow, and then harvest them and sell them to the General Store for a profit. Repeat this process, growing a greater variety of plants as you get more gold. As you do so, your garden will begin to attract and unlock pinatas.
Purchase 8 Sour Blocks from the general store. Once you've bought them all, you'll complete the Tower of Sour and unlock otherwise inaccessible pinatas.
Gain levels. Every time you harvest and sell a plant, you gain gardening experience. With enough experience, you gain a level. Some pinatas aren't unlocked by having particular plants in your garden, but rather by having a high gardening level. For instance, the Sour Shellybean arrives once you have reached level 4.