Berries in Pokémon Brilliant Diamond and Shining Pearl are essential for your Pokémon if you want to increase its specific traits, such as friendship, happiness, or even to keep them for use in battle. You can find berries throughout your Pokémon journey, and they are everywhere. But you will need a watering can to water them. This is what the Sprayduck key item can get in Pokémon Brilliant Diamond and Shining Pearl.
You will be able to find it once you get to Floaroma Town. When you get to the city, you will find a large building in the northern part of the map with two berry bushes on either side. Enter the building and speak to the woman on the left side of the room. It will immediately give you your Sprayduck key item without having to do anything for it.
Now that you have the Sprayduck, you will be able to walk up to any berry bushes you have planted and water your plants. You’ll want to water the berry bushes to make sure the plant is fully grown in about 24 hours and has more than two berries attached. The more frequently you water the berry bushes, the more berries they will have when they are ready.