Wait until the flower petals have faded, dried, or dropped
Use clean, sharp pruning shears or scissors
Follow the stem down to the first set of healthy leaves or a side bud
Cut just above that leaf node or side bud
Remove the spent flower head completely
Repeat regularly during the blooming season
Deadhead every few days to encourage more blooms
Leave some seed heads in late season if you want birds to feed on them
Remove all dead flower heads at the end of the season if you want a tidier plant
Dispose of cut flower heads if they are diseased or infested