Instructions
Press "X" on your Xbox 360 controller to open your main menu. Use your directional pad (D-pad) or left analog stick to select the village and press "A." On the PC press "F2" to open the village menu.
Use your D-pad or mouse to select the "Miss Petula's Paper Pets" shop in the Village. Click or press "A" to select the Rashberry in the shop inventory menu. You must be at least a level-12 gardener to purchase a Rashberry. They cost 1650 chocolate coins each.
Select a location in your garden with your mouse or left analog stick and left-click or press "A" to place the Rashberry. You can buy as many Rashberries as you have chocolate coins to purchase. Once you have multiple Rashberries in your garden, you can romance them to obtain additional Rashberries. The romance requirements for the Rashberry are one rotten hazelnut, one rotten gooseberry, one rotten chili and a Rashberry house in the garden.