Hanging annual flower baskets are fertilizer hogs. There are so many recommendations on what to use for fertilizer, from long acting fertilizers to making a tea solution. Probably the best fertilizers are the fast acting ones like Miracle Gro. Once the plant starts filling the baskets, it may be necessary to fertilize them at least once a week or more. Google fertilizing hanging baskets and see what type of fertilizer appeals to you. If you want your basket to look like the ones you see hanging from the light poles in cities and villages, you are going to have to fertilize and water faithfully.