Carex is a grass alternative that is a problem-solving native perennial for any home landscape. But with so many Carex species and cultivars to choose from, it’s hard to know what the best fit will be for your garden. To determine the most adaptable, resilient, attractive and ecologically valuable Carex species, Mt. Cuba Center spent several years trialing Carex plants, and this week on the podcast, my guest Sam Hoadley shares what they learned.
Sam runs research trials at Mt. Cuba Center — my favorite public garden — in Hockessin, Delaware. The garden’s focus is on native plants and their conservation, which is also Sam’s interest. Sam is originally from North Central Connecticut, where his love of native plants began. He walked in the woods with his mother and was given free rein in the home garden. Visits to public gardens such as Longwood Gardens in Pennsylvania furthered his interest. He got a degree in sustainable landscape horticulture from the University of Vermont and went to work at Longwood for several years before applying to join Mt. Cuba Center.
In 2018, Mt. Cuba Center promoted its trial garden manager, George Coombs, to director of horticulture, and since Sam had always admired George’s work and had used George’s reports, he was excited to apply to become Mt. Cuba’s next trial garden manager.
“It is the coolest job,” Sam says. “I get to learn every day. I get to be surrounded by native plants, and I get to really learn them in a really intimate way, which is really fun. And then you get to teach others and help people make good, informed decisions when they’re gardening with natives, and it’s a lot of fun. I think it’s the best job in the world.”
Mt. Cuba Center’s trials are thorough, and its research studies are detailed. The trials run for three to four years with a full-time staff plus volunteers. They produce outstanding data and share reports — for free – that become valuable resources for horticulturists. These multiyear trials require a significant financial commitment, so bravo to Mt. Cuba Center for taking this on and providing this valuable service.
“It’s a great way to motivate change,” Sam says. “If we can provide people with the tools that are necessary to make good, informed decisions, both in the nursery industry and as homeowners, we can help drive change.”
It’s a virtuous cycle that motivates conservation action. When people add great native plants to their home gardens that look beautiful and attract wildlife — and don’t require a lot of maintenance — they will be inspired to add even more native plants, Sam says.
Before proceeding any further, I’d like to pause to remind you that I have a new book out, “The Vegetable Gardening Book: Your complete guide to growing an edible organic garden from seed to harvest.” This book has insider tips and new-to-you information that will help you step up your gardening game and tackle challenges.
A Brief History of Mt. Cuba Center
Whenever I need a pretty picture of a native landscape or a natural-looking landscape scene, I just go to my archives of all the pictures I took during my many visits to Mount Cuba Center because there’s no shortage of spectacular, beautiful native plant scenery with majestic trees, tall canopies, and woodland mulched paths.
Mt. Cuba Center was the estate of the Copeland family before it became a private nonprofit foundation in 2002. The Copelands had come to Delaware in the 1930s from Litchfield, Connecticut, and built their home and gardens on a fallow cornfield. They had started out with formal gardens and more naturalistic gardens, and in time, wildflowers and native plants became their focus.
“They wanted their gardens to be centered around not just the beauty of these plants but conserving those plants in their gardens,” Sam says. “And they also soon realized that they wanted Mt. Cuba Center to be open to the public someday. They wanted people to be able to come to the gardens and they wanted people to be inspired by the beauty and value of native plants and hopefully inspire people to become conservators themselves.”
The long-standing naturalistic gardens include mature trees and wildflowers that have been in the ground for decades, and in 2013, Mt. Cuba Center officially opened to the public.
“Even though we’re a newer public garden, these gardens are established, they’re spectacular, and you can see all of these native plants all in one place — this very beautiful, naturalistic setting,” Sam says.
Mt. Cuba Center Trials
Even before a trial begins, it takes two or three years of planning. When choosing which plants to trial, Mt. Cuba Center staff consider which are readily commercially available so gardeners can make informed decisions, and they also consider that there are some plants that are not popular but could really use a champion.
At times, Mt. Cuba Center introduces gardeners to species they may not have seen before. If Mt. Cuba Center can show how special a plant is from a horticultural perspective as well as an ecological perspective, interest in that plant can really take off.
“If we start seeing species that are really exceptional, then we might try to make those species available to the commercial world so hopefully they’ll be available to home garden some in some fashion,” Sam says.
In most of its trials, Mt. Cuba evaluates a single genus and as many species and cultivars that fall within that genus. For herbaceous perennials such as Carex, the trial period runs three to four years. For woody shrubs, which the center is new to trialing, the trial period is about five years and still going. “Oftentimes in those later years, you start to see things that you wouldn’t have necessarily seen in those original three years,” Sam notes.
In the first year, the staff ensures the plants get established by giving them supplements during dry periods, but in subsequent years, they are hands-off so the plants are largely on their own and will accurately show how they can be expected to perform when they are not being coddled with water, fertilizer and pesticides.
“We jokingly call ourselves the worst gardeners in Mt. Cuba Center because we really want to see how these plants are going to do with very low inputs,” Sam says.
Data is collected during the growing season, typically from May through September, and even earlier or later for plants that work on different timelines.
“During that growing season, we’re observing all these plants on a weekly basis,” Sam says. “… Each week we are measuring these plants, we’re observing them, and we’re also assigning ratings on several different categories.”
The ratings, from 1 to 5, include the overall plant — the habit, the foliage, the form — the blooms, the length of the bloom time, flower coverage, hardiness, disease resistance, etc.
The scores are averaged in a weighted fashion to determine yearly scores, and the yearly scores are averaged for final scores. Most plants Mt. Cuba promotes earned scores of 4 or 5.
Sam works with trial garden assistant Laura Reilly on the ratings, ensuring they are on the same page, so what seems like a subjective score is calibrated for consistency and desirable plant traits.
While Sam and Laura evaluate plants from a horticultural perspective, the Mt. Cuba Center Pollinator Watch Team, consisting of volunteer citizens scientists, collects data from an ecological perspective,
“The value of native plants is incredibly important in our trials, and we’re trying to determine which plants, which species and cultivars may be able to support insects and wildlife the best when you select those for your home landscape,” Sam says.
You can download the entire Mt. Cuba Center Carex Research Report and review the results.
Getting to Know Carex
Carex is the largest genus in the Cyperaceae family, which is known as the sedges. There are hundreds of species of Carex native to North America, and a couple of thousand species worldwide. They are grass-like, cool-season perennials.
“This is an incredibly diverse genus. and there are plants that occur in every habitat, almost every habitat conceivable,” Sam says. “You can find Carex in alpine zones, you can find them in kind of wet shady woodlands. You can find them on sand dunes. So there really is — because there’s such a wide range of species and they’re all adapted to different conditions — there really is a Carex for every single landscape.”
Sedges can be distinguished from grasses and rushes by cutting the stems. Sedge stems are triangular and solid on the inside, while rushes have round, solid stems, and grasses tend to have round hollow stems and swollen nodes.
Sedges also have nodes, but they are subtle nodes. Located on the flowering stems, the nodes are just a slightly darker line, but in grasses, the nodes look like the stems are jointed.
Carex plants are really noted for their foliage, which comes in a variety of textures and widths, Sam says. “Some of them are deciduous, some of them are more on the evergreen side, but they really do provide that beautiful grassy texture in shade as well as sun.”
Carex does bloom, but that’s not what it is known for. Gardeners love Carex for its versatility, hardiness, and adaptability. Cares can also create good habitat and be an effective turf lawn replacement.
“They can cover ground, they can suppress weeds. I think about them as kind of a backbone to a lot of plantings,” Sam says. “And what we found in the trials is that they’re incredibly able to handle adverse conditions even conditions that you may not expect to see those plants in. Outside of where you would typically find them in the wild, they actually performed extremely well in many cases because we evaluated all these 70 different Carex in shade as well as sun, and a lot of them proved to be extremely adaptable to both conditions.”
No matter where you live, whether your soil is sandy or it’s heavy, whether you have sun or shade, there are options for you.
There are many widely available varieties of Carex available but not much information about how to use those in the home landscape,” Sam says.
In Mt. Cuba’s recent Carex trial, they included some species that aren’t commercially available but are local to Delaware.
“We wanted to show people that these species exist and showcase the diversity of this incredible genus,” Sam says.
Some species of Carex are stiff, while others can be as soft as grass.
Carex eburnea, for example, has a very fine texture, is low growing and can grow in very dry conditions. “It looks quite a lot like fine fescue, so until those plants bloom, sometimes it can be really difficult to tell the difference.”
As cool-season perennials, Carex plants do the bulk of their growing during the spring and fall. Their foliage, roots and rhizomes grow on the bookends of summer. “It’s surprising how much growth they are continuing to do during the summer, but it’s not where their growth is concentrated.”
The cool seasons are ideal for dividing Carex, because they can handle the stress then.
“Carex are not necessarily grown for their flowers, but there are some Carex species that the flowers are spectacular and you should grow them for the flowers.”
Many Carex species bloom in late April through May, though some species bloom in mid-March or early July.
“The bloom period is generally pretty short, one or two weeks, and then the fruit starts to mature and the fruit tends to persist longer on the plants than the flowers will. So the flowers are beautiful just for a short window. The fruit can be ornamental for a much longer period of time, depending on the species.”
One species in the trial, Carex durieui, blooms in late July and early August, which came as a surprise.
There are a lot of little surprises in the Carez trial as far as flowers and fruit, Sam says.
The winner in the Mt. Cuba Center Carex trial was Carex woodii, known as pretty sedge or Wood’s sedge, which makes straw-colored flowers from April through early May and has foliage with a blue-green hue. “It’s one of those plants that your eye is drawn to,” Sam says. Carex woodii puts up with full sun, shade and mowing, and the flowers are beautiful. It has a low-growing, slow-spreading habit like the popular Carex pensylvanica.
Carex pensylvanica “Straw Hat,” a selection made by Brent Horvath of Intrinsic Perennial Gardens, has beautiful flowers and would be a great complement to any spring perennials and ephemerals, according to Sam.
Carex woodii creates a denser mat that makes it better than Carex pensylvanica at suppressing weeds.
To grow a clone of a Carex plant you want more of, you can divide it. For propagation with less predictability than cloning, you can collect the mature fruit of Carex plants and plant the seeds found inside.
“You can increase the amount of Carex in your property relatively quickly by growing them from seed,” Sam says.
Planting Carex seeds is relatively straightforward, though some species require different treatments from others, he points out. Carex seed can be harvested in late summer or early fall.
All carrots have a swollen membrane called the perigynia around the seed.
“If you see that membrane that encloses the single seed or achene, you’re looking at a Carex,” Sam explains. “But if you remove that perigynium from that achene, often it takes a cool, moist stratification period, and then those plants will come up the next spring in many cases.”
He notes that with a genus as diverse as Carex, there will be exceptions and different seed preparation requirements.
A resource Sam really likes for Carex seeds is Prairie Moon Nursery. “They do a really good job of not just supplying the seed, but telling you what to do with it once you have it,” he says.
Carex as a Lawn Alternative
Carex is becoming one of the go-to plants as a lawn alternative, so in the fifth year that Mt. Cuba Center was trialing Carex, they subjected the plants to mowing.
“We really wanted to see if all these 70 different Carex species and cultivars could a tolerate mowing, and if there were any that actually kind of looked the part — could be a suitable alternative to traditional turf grass lawns,” Sam says.
After mowing the plants down to 4 inches every two weeks, from May to August, they found that most of the plants could tolerate mowing really well.
Certain plants, including Carex woodii and Carex pensylvanica, not just tolerated mowing but looked great. These are plants that are lower growing, with finer texture, and they really look the part of a turf grass lawn.
“Carex really offer you some unique opportunities, and I think that they could be really well suited to replace turf grass lawns in kind of trouble areas,” Sam says. These include areas of dry shade, such as around the root zones of maple trees.
“Carex, I really think of them as kind of a problem-solving plant,” Sam says. “If you have a difficult area in your landscape, there’s likely a Carex that can fix that problem for you.”
A Carex doesn’t have to be mowed to replace a turf lawn.
“There are lots of low-growing plants with fine textures,” Sam says. “You can have a beautiful naturalistic no-mow lawn that you can mix with other low-growing perennials, and not just using one Carex species. You can mix them. There’s a lot of opportunity to play with this concept and to really do some really cool stuff.”
There are Carex species native to all 50 states, so wherever you live, you can grow a disease-resistant, resilient Carex that doesn’t require fertilizer to thrive.
If you are tired of Vinca minor or English ivy in those dry shade areas where turf grass just won’t grow, Carex will make an outstanding groundcover. The verticality, spikiness and pluminess of Carex makes it a beautiful plant, especially en masse and when mixed with other species.
Carex as Specimen Plants
Carex are extremely ornamental on their own, and though sometimes they’re thought about as a companion plant or background plant, there are Carex varieties plants out there that are just striking on their own, Sam says. “You could include them in a traditional border and they would hold up to that, so there is, again, a Carex for every single garden, every design niche.
Carex also have an attractive texture and are just begging to be touched — though Sam warns that some Carex species do have sharp edges.
Carex for Ecology
Mt. Cuba Center’s Carex trial also examined the value of native plants as far as how many insects a plant can attract and support.
Because Carex are wind pollinated, they don’t have the same interaction with pollinating insects as, say, Echinacea and Hydrangea do, Sam points out. But they are still providing ecological value.
Carex provide cover that helps to preserve humidity at soil level, so a number of invertebrates — mollusks, insects, etc. — used Carex as cover in the trial garden.
Carex seeds provide food to birds, mammals and seed-eating insects, and the plant foliage is host caterpillars of a number of butterfly and moth species.
Mt. Cuba is now moving on from Carex trials to milkweed and fern trials, which I can’t wait to hear the results of.
If you haven’t already listened to my conversation with Sam Hoadley about growing Carex, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Do you grow Carex or another lawn alternative? Let us know in the comments below.
Links & Resources
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