Plants are trying to live their lives, not just please a gardener. They flower and go to seed. The seeds are their next generation, and they receive energy from the plant. If you want your garden plants to go on growing and blooming, you need to trim off the seed heads (unless you wish to collect and grow those seeds). This makes the garden look neater and diverts energy away from seeds and into fresh roots, leaves, and flowers. Just a few straggly seed stalks or pods can make a garden look untidy. If you don't notice it at first, take a photograph and check it out.
However, deadheading can sometimes be carried too far. Seeds of rudbeckia and other meadow plants can feed our songbirds, and seed plumes of sedum and ornamental grass can become attractive garden features in winter.
With reblooming roses, you'll want to remove the spent flowers in the early summer to promote a new crop of blooms. But in late summer or fall you may choose to leave them in place to make fat orange pods (the rose hips) for winter ornament.
Deadhead hybrid rhododendrons and mountain laurels to increase next year's bloom. Once the flowers begin to fade, use your thumb and forefinger (or small needle-nose pruning shears) to cut off the soft, immature flowering cluster. Just be careful not to damage nearby buds or shoots, which will soon be sprouting into new branches.
Keep reading to learn about how to stake plants.