The act of removing dead flowers is called deadheading and is done after the flowers are finished blooming and begin to fade. Deadheading encourages most flowers to produce another set of blooms instead of using energy to produce seeds. In fact, some flowers, especially annuals, will grow several sets of blooms in one season. Note that not all flowers will bloom again, such hydrangeas and forsythias, although deadheading will make the plants look nicer.
Cut off flower tops back to the first leaf node or new bud growth. Do this right as they begin to wilt and die on plants such as petunias, lilies and cone flowers.
Cut off dead flowers near the bottom of the stem with hand clippers on plants, such as hostas, bleeding hearts and amaryllis, that do not grow additional flowers on the same stalks. Do this as soon as the single or group of flowers die.
Limit your deadheading on flowers that have attractive seeds, such as autumn joys and purple emperors, which adorn the garden in the fall and winter. Also, if you're not sure if your plants will flower a second times and you want to collect the seeds or allow the seeds to spread, then only deadhead 50 percent of the flowers and take note for next year.