Many annuals look a little tired by September. Try cutting them back by a third to bring them back to the size and shape of the arrangement intended and encourage thicker growth. Coleus, Impatiens, Irisine and Persian Shield are some annuals I trim to improve the fall display.
Try putting the cuttings in a flower arrangement. Some will root. Pot them up to extend your enjoyment of your annuals indoors as the temperatures drop.