Some plants need to have their flowers removed in order to keep producing blooms. Here's a list of flowers that need deadheading as well as some that don't. My grandma taught me this when I was a little girl. She called it "pinching back".
You can often prolong bloom by removing spent flowers, but that's not true for all flowering plants. When a flower remains on a plant, the plant's energy is diverted into producing seed, rather than more flowers. Deadheading (removing the spent flower by pinching off or cutting back) is a must for many annuals but not all. With perennials, which generally have a shorter bloom period, deadheading usually isn't necessary but is used just to keep the plant looking tidy.
Plants that need deadheading:
- petunias (species and older varieties)
Plants that don't need deadheading:
- celosida (plume and wheat types)
- verbena (groundcover types)
- Wave petunias and other new petunia varieties