Answer: Deadheading serves two purposes: it keeps plants looking attractive, and it stops seed production. (Once a plant produces mature seeds, flowering declines.) Different plants respond to different methods, but the general rule is to remove spent blossoms, making sure you also remove the developing seed pod, often located at the center or just behind the flower. In other words, don?t just pull off the petals.
Zinnias, marigolds, and cosmos will flower all summer if you continually remove spent flowers. Cut the stem back to the next bud or set of leaves. Snapdragons will usually produce flowering side shoots if you prune off the main flower stalk once it has flowered (although the plant prefers cool temperatures and may not reflower in hot climates.)
Some plants, such as impatiens, naturally drop their flowers and don?t need deadheading. And although perennials generally have a shorter bloom period than annuals, you can still extend the bloom time for some perennials, such as black-eyed Susan, by deadheading.
Finally, some plants, such as sweet William, can be cut back after blooming and will produce a second flush of blooms. Simply shear the plants back to about half their height after their blooms begin to fade.
Hope this clarifies things for you!
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