The term “deadhead” simply means to take off the old, spent flower. When the bloom is finished the plant then sends its energy to making seeds. If you deadhead, you force the plant to flower again and prolong the length of time the plant gives flowering blooms. Some plants only flower once a year, but there are many annuals and perennials that benefit from deadheading.
Annuals like Petunia, Geranium, Alyssum, Cosmos, Lantana and Marigolds all respond very well to deadheading.
Daisy, Coneflower, Lupine, Phlox, Delphinium, Salvia, Veronica, Gaillardia, Yarrow, Coreopsis, Dianthus and Penstemon are examples of perennials that have a tendency to re-bloom. Often, the second blooms last longer.
You can deadhead from spring through autumn. However, if you like to leave seed heads on through the winter it is a good idea to stop deadheading in late summer. There are many plants that provide interest for us through the winter in addition to seeds for birds.
It may seem like a task that will never end; the new blooms and tidy garden appearance should keep you going!
A side note, if you love a particular plant, save some of the deadheads and keep the seeds until fall when you can sow them again!
The process of deadheading is very simple. Pinch, pull or cut below the spent flower and above the closest set of leaves. Sometimes, if the flowers are similar in age the easiest way is to shear the flowers off all together.