Deadheading is the removal of spent flowers. For many annuals, perennials, and roses, it is an important gardening chore. Deadheading improves the appearance of many plants, encourages the formation of additional blooms, and prevents the development of unwanted fruits or seed pods.
Annuals
Pinch off the faded flowers on annuals, such as geraniums, marigolds, zinnias, cosmos, pansies, and snapdragons, on a regular basis to prevent seed formation and promote additional flowering. Deadheading annuals can also improve the overall appearance of the plants.
Annuals like coleus, polka dot plant, and caladium are grown for their attractive foliage and the flowers can distract or be unsightly.
Impatiens, many petunias, and a few other annuals are self-cleaning and don't require deadheading.
Perennials
Deadheading perennials can have several benefits.
Extends the Bloom Period
The flowering period of many perennials, such as coreopsis, garden phlox, shasta daisy, and yarrow, can be prolonged by deadheading.
Promotes Re-Bloom
Delphiniums, salvia, and catmint often bloom a second time in late summer if the initial flower stalks are cut back after flowering.
Improves Vigor and Establishment
Removing spent flowers on daffodils, peonies, and bearded irises promotes plant vigor by preventing the formation of seed pods. Instead, the energy that would have been spent on seed and pod development is used to grow stronger root systems or bigger bulbs that will produce better flowers the following year.
Improves Appearance
Removing the flower stalks from perennials like iris, Asiatic lily, liatris, and hosta can make the plant look better for the rest of the growing season by removing stalks covered in brown or dead blooms and pods.
Prevents Self-Seeding
Some species produce abundant seed that readily grows in different areas in the garden. Sometimes this reseeding is "polite" and a welcomed addition to the garden. Other times it becomes overwhelming and invasive. Deadheading also prevents the self-seeding of golden marguerite, yarrow, columbine, blackberry lily, garlic chives, and other potentially invasive perennials.
Roses
Hybrid Teas, Grandifloras, & Floribundas
Modern roses, such as hybrid teas, grandifloras, and floribundas, should be deadheaded to conserve energy and encourage repeat bloom. During the first growing season, remove the faded flowers above the uppermost 3-leaflet leaf. Removing a larger amount of foliage reduces the young plant s ability to manufacture food and may slow its growth.
When deadheading established roses, the stem may be cut back to a 5-leaflet leaf. Retain at least two 5-leaflet leaves on each shoot. Using hand shears, cut about 1/4 inch above the leaf with the cut parallel to the leaf's angle. Stop deadheading hybrid teas, grandifloras, and floribundas in late summer (late August or September). The development of rose hips (fruits) slows plant growth and helps prepare the plants for winter.
Shrub, Landscape, & Old-Fashioned
Shrub or landscape roses rarely need deadheading, but doing so may improve appearance and promote even more blooms throughout the summer. There is usually no need to deadhead old-fashioned roses as many are one-time bloomers. Plus, the hips of some are quite attractive.