By Martha Engelke, EMGV
Deadhead and Cutback. You might think that these terms describe a new rock band or how you feel after a bad haircut. In reality they are tools for prolonging blooms and strengthening flowering plants. Deadhead(ing) is the process by which old growth and seed heads are removed from a plant to promote new growth and re-flowering. Plants are programmed to make seeds, bloom, and then set seeds. When you cut the blooms, the plant thinks it needs to make more flowers to create the next generation. Deadheading redirects plant energy from seed production to root growth and the production of more flowers. Cut(ting) back refers to the removal of buds early in the growing season to promote stronger and more abundant blooms later in the season. As Figure 1 shows, deadheading can be done in different ways. Sometimes jut the spent blooms are removed and at other times the stems are cut to open up the plant and increase the hardiness of the stems left behind.
There are several reasons to deadhead. Among the most common are to increase blooms, to prevent self-seeding, or to tidy up a garden. Your purpose will guide the type and extent of deadheading you do. Before beginning, it is important to know which plants will benefit from deadheading. Some annuals like summer snapdragon (Angelonia angustifolia) and wax begonias (Begonia semperflorens) do not need deadheading while others annuals like pot marigold (Calendula officinalis), bedding dahlia (Dahlia pinnata), pansy (Viola tricolor), and zinnia (Zinnia elgans) will bloom longer and better with deadheading.
Perennials that benefit from deadheading include bellflower (Campanula spp.), beebalm (Monarda didyma), and pincushion Flower (Scabiosa spp.) Other perennials such as echinacea, rudbeckia, and aster bloom longer with deadheading, but spent blooms are great for attracting birds and provide a valuable food source. In this case, you might not want to do aggressive deadheading.
Many perennials will rebloom with a good haircut after the first bloom although the second set of blooms might be smaller or sparser. Plants like dianthus (Dianthus spp) and daisies (Asteraceae) will bloom a second time if the flowers are cut back after the first bloom. Other plants that rebloom after deadheading the first set of blooms include verbena, delphiniums, salvia, and catmint (Nepeta), veronica, and coreopsis.
Another reason to deadhead is to control plants that are aggressive self-seeders. Depending on your goal for your garden, this may be a good thing or an annoyance. For example, native columbine (Aquilegia canadensis) is a prolific self-seeder and new plants can be found at a distance from the parent plant. If you want the plant to fill in sparse areas or you want to provide nectar for bumblebees, butterflies, and hummingbirds then you may choose not to deadhead. However, if it is getting out of hand and interfering with other pollinating plants, you might want to cut it back after it flowers and before it sets seed. Other perennials that are aggressive self-seeders include garlic chives (Allium tuberosum) and yarrow (Achillea).
Thinning is a process related to deadheading. When thinning, remove 1/3 of the plant’s stems at ground level when the plant is 1/4 to 1/3 of its mature size. Thinning has many benefits. It increases air circulation and light levels between stems to prevent powdery mildew and other diseases. Removing weak stems also makes the plant sturdier and may increase bloom size. The stems chosen should not be all in one place but distributed throughout the plant. Flowering perennials that should be thinned include peach leaf bellflower (Campanula persicifolia), beebalm (Monarda didyma), and coneflower (Rudbeckia spp.).
While deadheading refers to the removal of old blooms, cutting back refers to the removal of buds and stems before blooms occur. If you have ever been dismayed at how your garden mums get thinner and leggier every year, it may be because they need to be trimmed back early in the season before they bloom. Plants that respond well to cutting back include chrysanthemums (Chrysanthemum spp.), asters (Aster spp) and phlox (Phlox spp.) Cutting back should begin in early spring and be discontinued by early July. Once a plant is cut back , new lateral stems will grow from the stem that was cut and each of these lateral stems usually set flower buds.
After you have given your plants a good home with the proper amount of sunlight, nourishment, and hydration, remember that they still need friends to reach their full potential. Deadheading and cutting back can be great friends.
Iowa State University Extension and Outreach. Deadheading Herbaceous Ornamentals and Roses | Horticulture and Home Pest News (iastate.edu)
Michigan State Extension. Deadheading: Keeping your blooms blooming – MSU Extension
NC Extension Handbook: Chapter 10. Herbaceous Ornamentals. https://content.ces.ncsu.edu/extension-gardener-handbook/10-herbaceous-ornamentals
New Hampshire Extension What is the best way to deadhead perennials? | Extension (unh.edu) Penn State Extension Pruning Herbaceous Plants (psu.edu)To Deadhead or Not? Your Final Answer is… (psu.edu)
*The definition of deadheading and cutting back are not exactly the same throughout the literature. In this article deadheading is used to describe cutting of existing blooms, and cutting back is used to describe the cutting of buds and stems before blooming.
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