Dianthus is one of those annuals that really is not an annual. In our area it survives about three years with tons of color for most of the season. During the spring and fall it is covered with abundance of blooms.
During the heat of the summer it slows down the color show just a bit, and during the dead of winter it survives but with less color than other times of the year.
So for long living, excellent color displays and ease of care, Dianthus is one of the best buys for the dollar.