Calibrachoa are among the most commonly used sun annuals, and for good reason! The flowers resemble little petunias, they come in just about any color except true blue, and their trailing form makes them perfect for hanging baskets or spilling over the edge of planters. Calibrachoa will bloom all summer with enough sun, water, and fertilizer. If they get too leggy or out of control, you can cut the plants back by about a third.