WITH THE SURGE in interest in lawn alternatives and other native choices for groundcover, the genus Carex is always mentioned high up on the list. But which of these grass-like perennials, most of them labeled as best suited to shade, can actually substitute for lawn, and which sedges can serve other landscape roles? A four-year trial at Mt. Cuba Center in Delaware, the renowned native plant garden and research facility, sought to get at those answers and others.
Sam Hoadley is manager of Horticultural Research at Mt. Cuba, where he and the team trialed 70 different Carex over a four-year period. Sam’s report on the findings will be published on the Mt. Cuba website January 13.
Sam is also teaching a virtual class on February 1st on these important native plants. (That’s Carex haydenii, above.)
Before joining Mt. Cuba, Sam was lead horticulturist for Longwood Gardens’ hillside garden, and he received his degree in Sustainable Landscape Horticulture from University of Vermont.
Plus: Enter to win one of two tickets to the virtual event on Carex by commenting in the box at the bottom of the page.
Read along as you listen to the January 16, 2023 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).
top sedges and how to use them, with sam hoadley
top sedges and how to use them, with sam hoadley
Margaret Roach: Hi Sam, and welcome back. You’ve been hard at work as ever.
Sam Hoadley: Hi Margaret. Thanks again so much for having me. It’s great to be here.
Margaret: Well, I’m one of those crazy kind of people who looks forward to reports like these, because I just feel like I really want the lowdown, you know what I mean? It’s just there are so many choices in the world and especially now with native plants, there’s so little information on so many of them. So what you do is this amazing service to gardeners. So that’s how I regard it anyway [laughter].
Sam: Yeah, that’s the whole, it’s just helping people make good informed decisions because there are so many choices and we try to make the information for plants that’ll work for the most people available to nurseries and homeowners.
Margaret: So before we get started talking about Carex, about sedges: I think your February first online event is going to be really popular because it’s definitely a hot topic, because there are plants that we know, but yet we really don’t know them. They’re familiar looking, but which one is which and so forth. So that should be really interesting.
So a four-year trial, what were the aims? [Below, the shaded portion of the trial garden beds.]
Sam: So we were looking at these 70 different plants, a lot of which were commercially available, but some of which were locally native, mid-Atlantic region, and were provided to us by our state botanist Bill McAvoy, who is a Carex expert to say the least. And when we were really looking at these plants, we wanted to know how adaptable they were, how versatile they were. We were looking at them grown in full shade–or 60 percent shade, I should say–as well as full sun. We had a full set of Carex in both conditions. We wanted to push their tolerances, see how they would do in average garden conditions.
A lot of these plants you would see… You traditionally associate Carex–or at least what I had known about Carex when we first started this trial–with wet soils, you think of shade, but there’s a lot more to them. We wanted to unravel a lot of these common and some of not-so-common species and see how they would do in our trial gardens over the four-year period.
Margaret: As I said in the introduction, they’re sort of grass like perennials. There’s that little rhyming phrase. Sedges have edges [laughter].
Sam: Yes.
Margaret: So because since they’re grass-like, it can be confusing to tell them apart. What is it: “Sedges have edges; rushes are round; grasses are hollow.” Something like that.
Sam: Yeah, there’s a few versions, and the first two parts that rhyme almost always with the same. The last part in regards to grasses, there’s a few different versions of it, but some of the versions say grasses are hollow and we’ll talk about grass is having nodes. Carex have nodes as well, but grasses have these really swollen kind of joint like nodes.
Margaret: Yes.
Sam: But one of the best ways to tell most grasses from Carex is that they have a hollow stem that’s circular. Carex stems are solid and they’re triangular, as well as other sedges. And then deciphering whether that sedge is a Carex or not is the next step.
Margaret: Right. And we don’t even have to go there because I think it’d be a miracle if all of us gardeners and people interested in native plants for one reason or another could identify even a half-dozen let alone…you know what I mean? I have to acknowledge that I only know three really pensylvanica, which is all over the woodland edge of my property. So that’s been familiar to me for a long time. And then, plantaginea, whose species name, so Carex plantaginea I think means with the plantain-like leaf, right?
Sam: Yeah, exactly. Great species. Both top performers in our trial.
Margaret: And then the other one I know because when on the country roads around here, if you pass a wetland on the edge of the road, you’ll sometimes see what I always knew as tussock sedge which kind of stand-up like tussocks [laughter].
Sam: Exactly.
Margaret: “Little Miss Muffet sat on a tuffet” or something like that.
Sam: Exactly. No that’s-
Margaret: And wetlands. And that’s about, that’s Carex stricta, I think [below].
Sam: Yes.
Margaret: And that’s all I know. I don’t know any more of them [laughter].
Sam: And I’ll tell you what, when I started this trial, I would say I’m still not a Carex expert, but I’m fascinated by them and I’m learning more about them all the time. But when I started, I was probably pretty similar to where you are now. But seeing all these plants next to each other, it really helps untangle this seemingly complex world of Carex. And that’s something we really wanted to do for the audience as well, is that it can feel overwhelming and it can feel complicated, and we really aim, with this report in this trial, to decipher on this group of plants and try to make it manageable and digestible for people.
Margaret: Because people, gardeners, are looking for alternatives to lawn, as I said in the introduction, and for other groundcovers. And many of us, especially who have been at it a long time, the groundcovers that we planted years ago have turned out, many of them, to be kind of thuggish. They’re European or Asian plants that after a long time in the ground become too ambitious, too aggressive, we’ve got to get rid of them. People might have a bank that they want to underplant some shrubs or whatever on a bank, and hold the soil. They might want, again, groundcovers of various types.
So some Carex clump and some spread by rhizomes, is that correct?
Sam: That’s correct. And yes, some of them can spread quite vigorously, some a little bit more gently. But I would say that the portion of plants that spread by rhizomes rapidly in this trial was actually very low. I think we had four or five species that spread by rhizomes and eventually spread to cover larger areas. Most of the species in this trial were clump-forming. I think that would typically appeal to smaller home gardens just because these plants aren’t going to overwhelm or overrun the bounds of where they’re originally planted.
But a lot of the spreading plants won’t, either. Like you mentioned Carex pensylvanica, it’s a really great rhizomatous plant. It can weave its way amongst other perennials. It’s not going to overwhelm your garden. And I love it because it kind of fills gaps, it helps suppress weaves and it does just weave its way and forms that base layer of a planting.
Margaret: And so there are some that are thuggish, though?
Sam: There are a couple. And there were two species in this trial that I would label as aggressive. There is a place for those plants. If you have a small home garden, you have other plants, you don’t want being overwhelmed, maybe it’s not the right choice, but there are places where this could work. Those species could work really well if you were trying to stabilize a wet bank. Those two species that we trialed, Carex trichocarpa and Carex emoryi, would be really great options for wet, sunny meadows.
If you’re trying to out-compete potentially other invasive plants, adding those Carex species with other we’ll say “robust” native plants might be a really great way to naturally suppress unwanted non-native plants moving into those areas.
Margaret: And what about the range of size? Because the ones that I just mentioned that I know, they’re different sizes, they’re not all similar, and actually their foliage is different sizes as well. Like that plantaginea, the plantain-leaf one is quite different. It doesn’t have a narrow, a thin sort of blade-like leaf.
Sam: There’s a tremendous diversity of textures and habits and sizes within all of these Carex, even just within our trial, we had plants like Carex eburnea [above], which has very narrow foliage, less than a millimeter in width. And then we had other plants like Carex comosa, it almost looks like an iris, it has very broad foliage.
And then for sizes, we have plants that are several inches tall and that’s all they get to with clumps that are maybe 6, 7, 8 inches wide. I’m thinking of Carex eburnea again, that’s one of the smaller species in the trial. There are others that are 2 to 3 feet tall. Some that spread vigorously like Carex emoryi, Carex trichocarpa. And in the report we tried to simplify this a little bit, while we do have the measurements and the sizes, we did try to just categorize them into small, medium, and large. Just again to give you that quick reference where this plant might fit well into your home landscape.
Margaret: And so everyone thinks of them as foliage plants, kind of like grasses. And like grasses they do flower. And some of them I think have pretty interesting, almost spectacular flowers in a way, that some of the grasses that we call “ornamental grasses” also do in some cases. Do you know what I mean?
Sam: Oh, absolutely. No, there were some really beautiful Carex flowers, a couple that come to mind, like Carex woodii, which was the best Carex in our whole trial; the top-performing Carex. Its flowers are stunning. And a lot of Carex bloom kind of in this period between in late April, early May. There’s a few others that move into June a little bit. And then we had one oddball Carex that blooms in late July and August every year. But that’s the only one in our trial: Carex joorii, beautiful flowers, an unexpected thing when we first saw it.
But there’s a lot of Carex like Carex woodii, absolutely spectacular. Just masses of these kind of straw colored flowers that are kind of dancing above the foliage in early spring. To me, these are great companion plants for other spring ephemerals. They’re just a great complement. It’s not just a background plant, it’s actively contributing to the beauty and the design of that landscape.
Margaret: And so with native plants, the other thing a lot of times besides the look and the purpose and the size that we want to know in advance is do any insects or other animals used them as food or for any other purpose. I mentioned the tussock sedge [above, in bloom], Carex stricta, and in the nearby boggy sort of wetlands where I am in upstate New York and I know that bog turtles are, I think they nest or use them as like they’re a little [laughter] …, yes, I’ve heard that. So I’ve never actually seen one do so, but…
Sam: No, that’s absolutely true. And that’s one of the things we wanted to drive home with this trial as well. And a lot of our research, one of the things we’re looking at is not just the beauty of these native plants, but also the value of these native plants. And trying to tell people which of these native plants that we’re trialing that you could add to your home landscape and you’d be supporting wildlife.
And a lot of the trials we’re looking at pollinators. And with Carex, most Carex are not insect-pollinated. They’re wind-pollinated. So measuring their ecological value and their wildlife value in the trial was challenging. In the case of the Carex trial, we had a lot more anecdotal evidence of ecological benefit that these plants were offering.
We know in the wild that a lot of Carex act as host plants; there’s a lot of insects that will actually feed on the foliage, a lot of Lepidopterans that will feed on the foliage of Carex. A lot of wildlife, mammals and birds, will feed on Carex seeds. So they’re providing things even in your home landscape to wildlife.
We saw species of frogs and toads in the Carex trial. And we’re not really close to any source of water. And this was acting as a refuge, trapping that humidity at the soil surface and allowing these animals to have this refugia within the gardens.
But you mentioned the bog turtles, and that’s actually a really fascinating relationship that the bog turtles do have with Carex stricta. It happens in the mid-Atlantic as well. And Mt. Cuba’s actually been working with the state of Delaware for the past several years, growing Carex stricta to be planted back out into suitable bog turtle habitats. And we’ve actually seen the bog turtles nesting in those clumps of Carex stricta adding hatching clutches of eggs. So it’s been successful, it’s fascinating, and it’s a really great partnership with the state of Delaware that we’ve had for the last-
Margaret: Wow. That’s great. See, I’d heard about it, but as I said, I’ve never seen it. And it looks just like a nest; they really do. Tussock sedges look just like a nest. It’s perfect.
So they’re always on the list of shade plants. And so you said in the trials that you planted each species that you were evaluating in both a sun location and a shade location, a 60 percent shade location. And so, was that a big factor? Because people are looking for lawn alternatives, and normally people’s lawn is in some sun or even full sun. Was that one of the reasons you wanted to know that or?
Sam: That’s part of it,and we really just had to push their tolerances and see what they would be able to adapt to in average soils, in average garden conditions. And what we saw is that a lot of these plants are fairly adaptable.
They may be better suited or you may find them in the wild in shadier conditions, but if you give them enough soil moisture in just average garden soils, a lot of them do perfectly fine in full sun, and some of them actually do better, which was really great. And to me, that’s a great thing that you can look at a single Carex species, you can use that species to tie in two different garden situations. If you have a shady area next to a full sun area, you can use some of these Carex species to tie both of those garden areas together as a common element. And it really just showed how tough and adaptable a lot of these Carex are and how versatile they are. And there really is a Carex for any garden situation.
Margaret: Now we typically will see them sold as plants, not seed. Is that correct at this time?
Sam: Yeah. You often do see them sold as plugs, and established plants in quart pots and things like that. But there are good nurseries out there that are selling seed if you’d like to try to grow them from seed. Some of them have some interesting dormancies, but it’s not entirely too challenging to try at home either. Prairie Moon Nursery comes to mind, they have a really good selection of them.
Margaret: Oh yes, yes. Great. All right. And they probably have instructions because it’s probably not that just you’ve sowing the lawn seed and a few days later it starts to come up. It’s not quite like that.
Sam: Exactly.
Margaret: Right. But we’re learning more about that, I guess. So before we talk about some of the stars, I wanted to just digress for a minute more or two into… I think the last year of the trial, I think you did mowing testing or something [laughter]. And-
Sam: We did. [Above, mowing Carex woodii.]
Margaret: … I was laughing at that part of the report. I’m thinking I’m just seeing you all out there with your mowers, with these trial plots, wondering how these plants are going to look like with a haircut [laughter].
Sam: Exactly. No, so we done our four-year evaluation. The trial was essentially over, and the way that our trials are rotated in and out, we like to have every year you’re rotating out one. So in the case of the Carex, we wanted to hold these plants an extra season so that we would continue on that staggered schedule. So we had these plants sitting there and we were just like: What could we do with this? Is there anything else we eke out of this trial? Anything of value?
We decided: We’ve got the plants here, let’s mow them every two weeks. We started in early May, we ended in the end of August. And just let’s see what happens.
A lot of people are interested in Carex as a lawn replacement and there’s tons of Carex species that would be a great no-mow lawn replacement, essentially very little maintenance. You maybe only have to mow it once or twice a year. But we wanted to see if there was any that would be a suitable alternative to traditional mowed lawns, which I think in some situations are more aesthetically acceptable, if you will, in certain plantings. And just see how these plants responded. How tolerant were they; how would they do in full sun and shade? It was just a really interesting opportunity, and we’ve found some interesting stuff out of it as well.
Margaret: So which ones did well with being mowed, sort of looked O.K. and stood up to it? Which were some you would say, a couple that you would say, that were candidates for that, if one wants to put them in that situation?
Sam: Sure. A lot of the plants… And aesthetics is a big part of it, so plants that don’t just tolerate it but also look the part. The Carex really did tolerate it, were surprisingly tolerant. Even plants that didn’t really look like your traditional turfgrass. But a lot of these plants didn’t just tolerate it, but they looked good. They looked like your traditional turfgrass lawn at the same time, while having the added benefits of needing less inputs. We didn’t water these plants at all. We didn’t fertilize these plants at all. They looked good; they were healthy; they continued to grow. They were vigorous.
Carex woodii [above, foliage; in flower below] was one of those plants. It was not just the top performer in the overall trial, it was the top performer in the mowing trial, and looked great in sun and shade when it was mowed.This is just a spectacular species, and I’m really hopeful that this plant will take off in the nursery industry.
Carex eburnea I mentioned earlier. So that really fine-textured look, like a fine rescue, and it is clump-forming, but it spreads very slowly by rhizomes after it’s been established for a few years. So it’s one of those plants that you would need a few of them to fill an area. With Carex woodii what’s nice about that species is, it is rhizomes, it will cover ground slowly and will knit together and fill gaps. But Carex eburnea has the added benefit of being able to grow pretty well in drier soils. So if you have an area of dry shade, which is I think generally one of those areas that’s tougher for turfgrass lawns, this could be a really great candidate to replace turfgrass in those situations.
Margaret: Interesting. That would be something useful to have. Definitely.
Sam: Absolutely. And a couple other species, Carex socialis did great as a mowed plant. The mowed plants actually outperformed the non-mowed plants in our trial. Carex pensylvanica, as you mentioned, it was a great plant in the trial. Also great for mowing. I think whether we realize it or not, Carex pensylvanica is probably a component of many of our lawns, especially if we live in a naturalistic area. And Carex jamesii was another great plant that did tolerate the mowing and looked great at the same time.
Margaret: Oh good, okay. And I have a lot of the pensylvanica, as I said at my woodland edge and so forth, and just for maintenance purposes and to knock back any woody invaders that were coming in or successional things that were coming in, I used to in the early spring I would take one pass with tractor over them and they came right back. So would that be the time, if we did have a big swath of it, would a sort of a cleanup time, would that be the time that we did that to it, or does do they brown down? I can’t even really remember whether, I don’t think of them as looking all brown and dormant the way lawngrass does.
Sam: The pensylvanica [below] does, it is semi-evergreen. So basis of the foliage will remain green over the winter, and mowing them or cutting them back in late winter, early spring is a really great option. I think you can also do it in late fall or early winter. And I think that also has the added benefit of if you have Carex pensylvanica mixed in with other, say spring ephemerals or early spring perennials, if you mow it earlier in the year, any interference with those other emerging plants in the spring will be avoided by doing it earlier in the year.
Margaret: Right, O.K. So if you couldn’t be mowing because you’re waiting for something, some ephemerals to come up. I have it in one area where there’s a lot of Maianthemum, a little-
Sam: Oh, sure
Margaret: … woodland, beautiful little white, delicate native wildflower, and obviously I wouldn’t want to go with the tractor over those [laughter] early on and so forth. So you’ve shouted out some; what about plantaginea? Did that perform well at all? Because it has such a distinctive leaf. So tell us, would that be one, is that one that does have good uses because it’s so distinctive looking? Or what are a couple of other ones that you haven’t mentioned that you want to shout out?
Sam: Absolutely. So plantaginea [below] is a great species. We have it planted as a groundcover in certain areas in Mt. Cuba Center. We know it’s a great plant. It’s commercially available,. But its best feature is that broad corrugated foliage. It’s very striking and it blooms really, really early in the season, at a time when not a lot of else is happening in the spring garden, I’m talking kind of mid- to late March, these flowers are coming up.
And it’s one of those plants that it is semi evergreen and if you really site it in a protected shaded location over the winter, it is going to remain essentially evergreen over the winter. And it’s one you don’t want to cut back too much. It’s a little bit slow to respond and reflush new foliage, but it is truly a spectacular species. Definitely worth growing in any shady garden.
Margaret: I have it as the edge of some loose beds that are adjacent to some gravel and so forth and it just makes a soft loose edge and it’s very handsome. Those beautiful, fairly wide, as you say, textural leaves. It’s quite nice.
Sam: No, they’re lovely. And Carex woodii, as I mentioned before, really just an outstanding plant, has great foliage, great flowers, covers ground gently in a very similar category as Carex pensylvanica, but in my opinion, just a slightly better plant. It actually suppresses weeds a little bit better than Carex pensylvanica, if that’s what you’re looking to do.
One of the larger species that we really, really liked in this trial is Carex cherokeensis, very close to an evergreen plant as well. Larger species, you could use it in mass or even singly. It will really stand up on its own as being a specimen in your landscape. It did well in sun and shade, really just this deep green, lustrous foliage, really a spectacular species.
And Carex stricta and Carex haydenii, two very similar species, but two of my favorites. They have these absolutely spectacular displays of flowers in late April, early May, just truly stunning. It looks like a fireworks display. Both of them were exceptionally tolerant to shade and sun. Both of these plants, as we mentioned, really are very tolerant and even preferred very wet habitats. Carex stricta like you mentioned, grows in kind of these tussocks, little like self-made islands.
Margaret: Yes [laughter].
Sam: But they do fine in average soils as well. I don’t know how well they do in drier soils, but in the average soils of the trial garden, they performed really, really well.
Margaret: Interesting.
Sam: In sun and shade.
Margaret: Well, I’m excited to learn more and I started, as I said, reading the early version of the report, and I think your February 1st virtual event is so important for people to learn more about these plants, because they are such a great tool in the toolbox for this transition from away from some of our endless miles of lawn and other groundcovers that don’t serve any purpose really ecologically.
Sam: Exactly.
Margaret: So thank you, Sam Hoadley at Mt. Cuba Center. Thank you for the work and for making time today to talk, and I’ll talk to you again soon, I hope.
Sam: Absolutely. Thanks so much for having me.
more conversations on top native plants
Browse my past Mt. Cuba interviews about Echinacea, Hydrangea, Phlox, Monarda and more
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 13th year in March 2022. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the January 16, 2023 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).
