It’s simply the removal of mature/spent flowers that are turning brown or losing their petals. If left on the plant, most of these spent flowers will develop fruit/seeds. The developing seeds drain energy from the plant and induces a natural cycle of self death in annual/seasonal plants or dormancy in perennials/permanent plants. Deadheading interrupts this natural cycle, encouraging plants to continue to produce new buds, which prolongs the plant’s blooming period and that means more flowers for your garden.. the energy saved from going into the developing seeds also encourage branching and leaves formation, thus the overall look of the plant is improved..
Deadheading techniques vary depending on the growth habit of each type of plant. To deadhead, use a pair of sharp garden scissors or wire cutters to cleanly cut the stem of the dead flower.
Those annuals or perennials which bloom in clusters for e.g. Phlox, Ixoras, lantana, statice etc, removing individual flower is not possible so deadhead by removing the whole cluster when it looks unsightly, you may notice that 3-4 blooms may be present on it but the overall cluster wont be looking good..
As a rule of thumb, dont keep the bloom which is not looking good or it is smaller...
In many plants like petunia, nicotina, snapdragons, carnation, dianthus, pansy, sweetpea etc.. the seeds develop at the base of the flower, so removing the dried out petals will do no benefit to the plant, the whole flowering stalk must but cut off..
Some flowering shrubs can be deadheaded to encourage a second flush of flowers. Roses are a good example. Cut the flower stems to a lower bud or to the next set of five leaves or the large leaves. Not all shrubs respond to pruning with a second flowering period, but cutting off the browned blooms can keep the shrub looking attractive.
Once you get the knack, you’ll see how easy it is to keep your flower border blooming, especially if you walk through the garden regularly to snip off faded blossoms
and you’ll notice the difference in how tidy your garden looks, too..
My Gaillardias, which are weekly deadheaded:
This picture shows from where the spent bloom of petunia should be cut off (click to enlarge):
This picture shows proper deadheading of rose (click to enlarge):
I use this type of wire cutter fro deadheading:
