As flowers shed their petals and begin to form seed heads, energy is focused into the development of the seeds, rather than the flowers. Regular deadheading keeps the plants energy on producing beautiful flowers. Deadheading is the term used for the removal of faded or dead flowers from plants which prevents them from producing seeds. If an annual is allowed to go to seed the plant will stop trying to flower.
Most annuals and perennials will send up new blooms throughout the growing season if deadheaded. Deadheading is a very simple garden task. As plants fade out of bloom, pinch or cut off the flower stem below the spent flower, just above the first set of full, healthy leaves. Repeat with all the dead flowers on the plant.
By spending at least a short time in the garden each day or every several days, the task will not be overwhelming and your garden will look better for your efforts