Guest Author - Jessica Carson

The removal of spent flowers before they have a chance to set seed will often trick a plant into producing more flowers when it otherwise would not. The botanical purpose of flowers is for the plant to reproduce. Once that job is done there is no more reason to put energy into blooms and the plant's energy will be channeled to seed development. But if the blooms are removed the plant must bloom again in order to produce the seeds.

Different types of plant structures will benefit from different styles of deadheading. Some plants will re-bloom on the same flower stalk, others require the entire stalk to be removed for new flowers to form. Remove the spent flowers when they start to wither, discolor, dry out, or otherwise no longer look appealing. If you want your plants to set seed for next year, deadhead until late in the blooming season, then allow the last of the flowers to produce seed.

Single Flower Stalk
Some flowers, such as scabiosa, larkspur, columbine, bleeding heart, coral bells, and poppy, produce only one flower or compact group of flowers on a long stem from the base of the plant. If desired, trim single flowers to the main stalk until all flowers have bloomed. Once flowering is complete, cut or pull the stalk at its base where it emerges from the main plant.

Multiple Flower Branches on a Stalk
Some plants, such as chrysanthemum, cornflower, lupine, delphinium, and gaillardia, will re-bloom from offshoots from the main stalk. Cut flower stems back to just above the first set of small leaves or branches, where new bloom buds will form. Once the stalk has finished blooming remove it at the base.

Individual Flower Branches
Many types of plants produce flowers on short individual branches. Examples are marigold, and dahlia. Trim the stem of the spent flower back to the first set of leaves or to where it branches from a main stem.

Large numbers of Small Flowers
Some plants, such as coreopsis, alyssum, and lobelia, produce a large number of flowers. For these, wait until the majority of the flowers are finished and then trim off everything to encourage a new round of bloom production. Pansies and petunias will also benefit from a mid-season shearing as their branches get long and leggy.

Single Bloom Stalk Bulbs
Remove the bloom stalks from bulbs and rhizomes such as amaryllis, crocus, daffodil, gladiolus, iris, narcissus and tulip as soon as they fade. This allows the bulb to store energy for next year rather than expend energy in producing seeds. Trim the stalk back to the leaves where it emerges.

Rose
Prune the spent flower and branch back to just above the first set of five leaves. Some heirloom varieties will not re-bloom, but removing the spent flower will allow the plant to put energy into growth rather than rose hip production. If you want rose hips for tea or wild animal food, leave some spent flowers on the plant towards the end of the blooming season.

Not every flower will re-bloom if deadheaded. Most annuals will, some perennials will not, and single flower-stem bulbs won't. Here is a list of many common flowers and how they will (or won't) benefit from deadheading.
Note: If your flower is not listed here then experiment; it won't hurt the plant to deadhead and you may be rewarded with a re-birth of color.

Flowers that Benefit from Deadheading
Alstromeria – pull up on the spent flower stalk to remove it from the plant. Simply cutting will not stimulate re-blooming
Aster
Bleeding Heart
Buddleia or Butterfly Bush – flower removal and pruning after bloom will shape this vigorous grower and stimulate a new round of blooms later in the season
Calendula
Chrysanthemum
Coleus – pinch off flowers to encourage plant growth. Pinch tips off branches to encourage branching and full, dense growth.
Coral Bells
Coreopsis
Cosmos
Crape Myrtle – removal of spent flower clusters will stimulate a smaller second-blooming round.
Daisy (all types)
Daylily- snap off spent flowers from stems, remove stem at ground when all flowers have bloomed. Some cultivars will re-bloom.
Delphinium
Foxglove
Gaillardia or Blanket Flower
Hollyhock
Jacob's Ladder
Lavendar
Lupine
Marigold
Pansy-deadheading prolongs plant (and blooming) life
Petunia-allow to bloom and re-bloom naturally, then prune back long branches as the season progresses for renewed flowering
Rose
Salvia
Snapdragon-trim the bloom stalk just below the bottom flower/seed pod. New branches and flowers will form there
Viola-deadheading prolongs plant (and blooming) life
Zinnia

Flowers that don't require deadheading, though removing spent flowers may improve the look of the plant
Astilbe-leave dry flowers as long as they look attractive
Bea Balm
Begonia
Bougainvillea
Clematis
Dianthus
Euryops
Fuchsia
Hibiscus
Hydrangea – remove the flower clusters as soon as they fade.
Impatiens (all types)
Jasmine
Lantana
Lilac – remove flowers immediately after bloom to avoid damaging buds for next year
Mandevilla
Morning Glory
Nasturtium
Salvia
Trumpet Vine
Verbena
Vinca
Wisteria