Sweet William, or dianthus, is a gardener's favorite as it is easy to grow and is available in numerous colors. If you grow sweet William, you will want to deadhead them throughout the course of their blooming season. Deadheading is the act of removing fading blooms from the plant. It does not destroy the flowers, rather it helps promote healthy new blooms according to the National Garden Bureau. If you don't deadhead sweet William, it will sow hundreds of seeds that may eventually take over your garden.
Wait until after the first spring bloom before deadheading.
Watch for the flowers to start to fade and lose their bloom -- this is the time to deadhead sweet William.
Take your garden shears and cut off the bloom and the foliage. The place to do this is 2 to 3 inches above the ground at the base of the flower.
Leave the last set of blooms on the flowers at the end of the summer if you want them to reseed themselves for next year.