Hanging baskets that are filled with sun-loving plants will need watering daily, especially on sunny, warm days. They will also need to be fertilized with a liquid fertilizer at least once a week. Fertilizing encourages new buds to form and keeps them blooming all summer long. You can choose to feed them every time you water them but do it at a reduced rate. If you get to the middle of the summer and your petunias are getting too long, you can give them a haircut.