Carex for the Mid-Atlantic Region

By Katie Dubow and Mt. Cuba Center Staff

Carex is a large genus of grass-like perennials that are found in nearly all corners of the planet. Eastern North America alone hosts hundreds of species, although relatively few of these are available commercially. The genus Carex belongs to the Cyperaceae plant family. Members of this family are commonly referred to as sedges. Sedges may resemble plants in other families such as the Poaceae (grasses), but Carex have specific anatomical features, such as triangular stems and unisexual flowers, that set them apart.

The diversity of Carex matches the wide spectrum of habitats in which they grow, from shaded wetlands to coastal sand dunes and almost everything in between. In the garden, some Carex species are surprisingly adaptable to conditions outside of their typical wild preferences. Carex may be planted en masse to cover ground, stabilize soil, and suppress weeds, and some species are so striking that they can be used as individual specimens and accents. In a typical cultivated landscape, Carex are low-maintenance, requiring a late winter or early spring cutback, but many species thrive even without this level of care.

According to a four-year trial conducted by Mt. Cuba Center in Hockessin, Delaware, Carex are one of the most effective and versatile problem-solving plants for home gardens.

The trial evaluated 70 types of Carex, including 65 species and five cultivars native to the Mid-Atlantic region. Results are available now in the new report Carex for the Mid-Atlantic Region

Carex can be found in a wide range of habitats, and provide food and shelter for wildlife, as well as being a sustainable alternative to traditional turfgrass lawns.

Sam Hoadley, Mt. Cuba’s manager of horticultural research, ranked the species and cultivars based on plant vigor and foliage quality in both sun and shade locations. Carex woodii, or Wood’s sedge, was the top performer in the trial, demonstrating the genus’s ornamental value and versatility in the garden. It excels in both sun and shade and offers a carpet of straw-colored flowers from April to May.

“Carex are quickly becoming favored by homeowners and horticulturists alike, thanks to their beauty, utility, and overall minimal maintenance requirements,” explained Hoadley. “The diversity of the genus is outmatched only by the wide spectrum of habits in which they grow—from shady wetlands to coastal dunes, you can find a Carex to grow and thrive there.”

Hoadley added that not only do Carex provide food and shelter for wildlife, but they also proved to be an option for those looking to replace their lawns with a more sustainable option.

“How many perennial genera have members that we can recommend as successful and mowable replacements for traditional turfgrass lawns? That aspect alone pulls Carex into the longterm sustainability conversation,” he said.

Key Takeaways

• Carex woodii, or Wood’s sedge, was the trial’s top performer and exemplified the genus’s ornamental value and versatility in the garden. Although similar to C. pensylvanica in its low-growing, slow-spreading habit, C. woodii forms a denser mat of foliage, and is therefore, superior to suppressing weeds. It excels in both sun and shade locations and offers a carpet of straw-colored flowers from April through May.

• The trial’s top-performing species and cultivars thrive in average soils; i.e., their trial conditions were not considered too moist or too dry. But do not dismiss those without high marks as “underperformers.” These may, in fact, excel in landscapes with differing soil types. Those considering Carex species in their landscapes are encouraged to consult the “Carex for Dry Soils” and “Carex for Moist-to-Wet Soils” charts in the research report.

The Carex trials included a year-long mowing component and found a vast majority of types trialed were tolerant of regular mowing. Small- to medium-sized Carex with fine-textured foliage gave the aesthetic most closely associated with that of a traditional lawn. Those species with horizontally growing underground roots showed potential to fill in gaps within a lawn, as well as requiring fewer plants when installing a Carex lawn from scratch.

C. woodii is also the trial’s top-performing mowable sedge. Find the other top mowable sedges in the research report.

• While most Carex are wind-pollinated with little value for pollinators, Carex provide for other wildlife in a variety of ways. The seeds of Carex are eaten by mammals and birds and the leaves of Carex of consumed by caterpillars of numerous species of butterflies and moths. In some cases, the Carex themselves are the habitat, providing refuge for a diversity of organisms, both in home gardens and in the wild. Mt. Cuba is working with the state of Delaware to help expand suitable bog turtle habitats, and C. stricta is playing an important role as part of the turtles’ habitat.

This research report details Mt. Cuba’s top 16 Carex performers. Descriptions of all 70 plants included in the trial are available at mtcubacenter. org/trial.

Mt. Cuba Center is near Wilmington, DE (USDA Hardiness Zone7A/6B) and grows multiple plants of each taxa in a 15,000 sq. ft. trial garden that includes areas for growing both sun-loving and shade-loving plants. The clay-loam soil in the trial garden has an average pH of 6.5.

The trial garden is maintained with the home gardener in mind. Plants are watered as needed during the first year to get them established, but afterward they are left on their own. Pesticides are not used unless there is a serious threat to the entire trial’s survivability. Perennial plant trials usually run for three years to ensure the plants experience a variety of weather conditions. It is Mt. Cuba’s policy to replace dead plants after the first winter to compensate for poor establishment or initial plant quality. However, no replacements are made during subsequent years. Each taxa is evaluated weekly and assigned a rating based on a scale of 1–5 (5 being the highest rating). This rating takes into account many factors, including habit, floral display, disease resistance, hardiness, and foliage quality. The average of these weekly ratings is then used to calculate the final score displayed on Mt. Cuba’s website. o

Katie Dubow is president of the Garden Media Group, based in Kennett Square, PA . All photos on pages 14–15 are courtesy of Mt. Cuba Center

Top Carex Performers

• Wood’s Sedge (Carex woodii)

• Cherokee Sedge (Carex cherokeensis)

• Common Brome Sedge (Carex bromoides)

• Hayden’s Sedge (Carex haydenii)

• Upright Sedge (Carex stricta)

• Emory’s Sedge (Carex emoryi)

• Long-Beaked Sedge (Carex sprengelii)

• Pennsylvania Sedge (Carex pensylvanica)

• Straw Hat Pennsylvania Sedge (Carex pensylvanica ‘Straw Hat’)

• Little Midge Muskingum Sedge (Carex muskingumensis ‘Little Midge’)

• White-Tinge Sedge (Carex albicans)

• James’ Sedge (Carex jamesii)

• Oehme Muskingum Sedge (Carex muskingumensis ‘Oehme’)

• Fringed Sedge (Carex crinita)

• Leavenworth’s Sedge (Carex leavenworthii)

• Plantain-leaf Sedge (Carex plantaginea)

By Jessica Harden

Designing with purpose was the 2023 theme for the annual GreenScapes Symposium, held this year on February 17 online over Zoom. The annual program started in 2004 and focuses on the intersection of horticulture and environmental issues. It is hosted by Brookside Gardens and Montgomery County Parks. About 900 people, from all over the region and beyond, took part in the program this year.

The event started out with landscape architect and co-owner of Studio Sustena Laura Hansplant talking about “adaptive strategies for sustainable plant design.” Hansplant said that gardeners and landscapers typically focus on the initial outcome as opposed to long-term results.

For example, the industry focuses on using cuttings to propagate plants that look identical to each other and maintain uniformity. This lack of genetic biodiversity doesn’t mimic nature and makes plants vulnerable to disease. Instead, Hansplant said people should use seed-grown plants, allow plants to reproduce, and learn to value natural variation.

Sustainable plant design occurs when there is intentional replication of natural landscapes, Hansplant said. This will create low maintenance landscapes because reproduction will do the work.

“Carbon Sequestering Sites” by Panela Conrad followed Hansplant’s talk. Conrad is a landscape architect, founder of Climate Positive Design, and current Loeb Fellow at the Harvard Graduate School of Design. She created the Pathfinder app to help people measure the carbon sequestration of their designs so they can be more intentional with their sustainability efforts. Some of Conrad’s tips for reducing carbon footprints are to increase planting, reduce paving, and use lower-carbon materials.

Human activities threaten biodiversity, Conrad said. Efforts to protect the remaining biodiversity include conserving existing ecosystems, as well as soil biodiversity. Restore and repair soil by simply composting because 40% of waste in the United States is compostable. She also said people need to work toward carbon-smart planting design to work toward long-term goals.

Veronica Tyson-Strait, a landscape designer, educator, artist, and horticulture manager at Randall’s Island Park Alliance, talked about “connecting minority communities to the natural world.”

Immigrants who have left their home countries and are living in countries like Canada or the United States have an aversion to gardening and landscaping because it’s seen as something done by the poor, Tyson-Strait said. Doing those things, though, could help heal the trauma from leaving their homelands. Efforts to make these activities more accessible include advocating for more landscapes; adding planters, terraces, and green roofs to residential areas; and advocating for land equity because only 2% of farmland in the United States is owned by people of color.

Tyson-Strait said people can make their own landscapes feel more welcoming by including plants that are native to other countries. Plants like banana trees, red amaranth, and even potatoes can help people feel connected to the natural world because these are reminders of their home country, Tyson-Strait said.

The final speaker, Benjamin Vogt, is an author and the owner of Monarch Gardens. Vogt’s new book, Prairie Up, is an invaluable reference in sustainable garden design for those wanting both beautiful and functional landscapes. In a talk entitled “Lessons in the Design and Management of Natureinspired Landscapes,” he provided a unique perspective on who biodiverse landscapes are for.

While most gardeners say they plant those landscapes for wildlife, Vogt said it’s important to remember to also plant for people. Natural human instinct is to feel threatened by the hint of wildness that sometimes occurs in urban wildscapes. To prevent that, Vogt said to choose shorter species; only have three or fewer flowers blooming at a time; and include bird baths, walkways, or benches to show the design is intentional and meant for people.

Vogt also gave tips for dealing with the weed control department of a local county/municipality or the strict rules of a homeowner association (HOA). First, he said to stay calm and thank them for doing their job—they’re yelled at by other people all the time. Next, remember that city ordinances are vague, so officials can make case-bycase decisions.That makes it important to know the scientific name of every plant in the landscape, know what pollinators are present and their benefits, and be able to cite specific studies that show the benefits of urban wildscapes.

Biodiverse landscapes are beneficial for people, too, and can be welcoming if done intentionally. o

Jessica Harden is a junior journalism major minoring in law and society, with a concentration in criminal law, at the University of Maryland, College Park, MD. She is an intern this semester with Washington Gardener and is from San Antonio, TX