WHEN I SPOKE to naturalist and nature writer Nancy Lawson recently about her adventures in wildscaping at her Maryland garden, there was one topic in particular I wanted to double back to and dig in deeper to: her tactics for fighting unwanted weeds and invasives as we loosen up parts of our landscapes with more native plants.
I wanted to learn more about how to give the desired plants the edge, including some of the native perennials that have proven to be Nancy’s allies in out-competing the undesirables.
Nancy Lawson is author of “The Humane Gardener” and more recently of “Wildscape.” In that book, she stresses that we’re not alone out there, and promotes animal-friendly planting and maintenance strategies. She helps us tune into everyone whose home it is through a mix of findings from scientific research and her own intimate moments of discovery spent making her own wildscape.
Read along as you listen to the June 12, 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).
weed-fighting natives, with nancy lawson
Margaret Roach: Thanks for coming back to talk to me again, Nancy. Much appreciated.
Nancy Lawson: Thanks for having me. It’s great, and this is one of my favorite topics too.
Margaret: You like weeds, huh?
Nancy: I like native weeds.
Margaret: O.K. Yeah, because I’ve just gotten past having a garden open day. And so it’s sort of the spring drill of getting the garden, whether you’re literally having visitors or not, but getting the garden open—mulched, and cleaned up and whatever, whatever. And now it’s time, and I bet a lot of people are in the same boat. It’s like it’s time to double back and fight some of the bigger fights that I know we all face in one spot or another in our gardens [laughter]. We all have something. But what are some of your challenges there at your place? You have a couple of acres, similar-sized place that I do, and you’ve been there a long time. What are some of your constant undesirable companions?
Nancy: Yeah. Well, the stiltgrass [MIcrostegium vimineum] is one of them, because it likes to come up. It can make itself at home in tiny little pockets at pretty much anywhere. But another one that I recently had a very successful little battle against was mugwort.
Margaret: Oh, yes.
Nancy: Yeah. We inherited mugwort with some heirloom asparagus that my husband’s grandfather had in his garden, and my mother-in-law gave us some, and I had a feeling it was going to come with mugwort, and it did, and we didn’t manage it. And so it became a 30-foot by 10-foot space of mugwort after a time [laughter].
Margaret: Yes, yes. And that’s an Artemisia, isn’t it [Artemisia vulgaris]? I think. Isn’t it?
Margaret: Yeah, so it’s a perennial Artemisia, and it’s rhizomatous I guess, is that correct also?
Nancy: Yeah. So there’s these big orange-rooted mats when it really gets going. And I’ve had it in other places where there are already lots of plants, and in those places it’s very easy to just pull. But this was a place we had specifically dug out for asparagus, and not put much other things. And it was always just my last thing to get to because there was so much else to do. And whenever I would try, there were lots of ladybugs in there.
And then one year I noticed that there were walnut trees coming up in it, and there were black raspberries that actually really seemed to be competing with it. And so that gave me some encouragement. Those were my bright spots to start from. And I guess it was right before the pandemic when I started just taking it on for real. And I did a combination of smothering it with cardboard and wood chips and then also… But I don’t want to just do that because then stuff comes right back, you know?
So I also started planting other things that grew in a similar way, like Jerusalem artichoke, mountain mint [Pycnanthemum], these things that could really take over the ground in the shady part, the golden ragwort, the robin’s plantain [fleabane, Erigeron pulchellus], and these other things that would really either shade out germination of the mugwort seeds or compete directly with the roots.
Margaret: And so how did you kind of figure that out? Do you know what I mean? Did you just observe who was doing a good job elsewhere? Where do you get that kind of insight?
Nancy: So I started just looking at this sort of subject matter, I guess probably about 12 or 13 years ago when I had garlic mustard a lot in a certain area. And I left some plants out of golden ragwort [Packera aurea], and I was going to give them to friends. And then I came back the following spring. This was in the fall, I guess I had dug them up, and I found that they had rooted out of the pots and into the golden ragwort and saw they were competing with it.
And then I learned about plants like clearweed [above, as a groundcover at Nancy’s; detail at Margaret’s below], that actually there’s been research showing that they are… They can directly compete with garlic mustard chemically.
Margaret: That’s a great plant, Pilea pumila. It’s a great plant, and people think it’s a weed because it has that “weed” suffix in its common name, but it’s an important… For certain moths or butterflies, I believe it’s a host plant, and it’s a great plant.
Nancy: It’s beautiful.
Margaret: So it’s interesting to hear that it also has scientifically proven ability to help us with these types of problems.
Nancy: Yeah, it can go head-to-head. And so I guess seeing that sort of research makes you wonder, well, what other plants can do this?
Margaret: I see.
Nancy: And obviously the ragwort can do it, and then thinking about not just their chemical properties, but their growth habits. And one of the reasons that the ragwort does it, at least where I live, is that it’s also usually pretty evergreen. And so it’s competing probably not only chemically, but it also has this ability to leaf out before anything else, or already be leafed out, depending on where you live. And so it can shade out germination of the garlic mustard seed.
Margaret: Well, and that’s how a lot of our what are now considered invasive plants in many areas that came from other nations, that was one of their traditional sort of edges, why they became so successful when they came here, and similarly where our plants went to other places as plants have moved around the world, is that they frequently leaf out sooner than the local stuff [laughter].
Nancy: Yeah, exactly.
Margaret: And that’s a great… You’re right, that’s a great… So looking for those types of qualities, but not in an invasive obviously, looking for those kind of qualities that can help to stifle the unwanted. I see. So that’s what you were kind of doing.
Nancy: Yeah. Exactly.
Margaret: Because some of these weeds that you’ve mentioned, they have different tactics for succeeding as weeds. I mean, the stiltgrass, it’s a warm-season annual. It makes a lot of seeds per seedhead, a lot. They can reside in the soil for three to five years and stay viable. And there’s a lot of qualities that make it succeed and outsmart us.
Nancy: [Laughter.] Right, which you have to admire.
Margaret: Well, weeds, yes, they’re incredible. Garlic mustard has so many tactics. It’s allelopathic; it exudes a chemical into the area where it grows that deters other plants from getting a foothold. It’s got a great deep root. It comes up early. It’s a prodigious sower of seeds. These are these tactics, and so how do we one better them? Right? Is that what you’re looking for, plants that are even “smarter”?
Nancy: Yeah, or at least they can hold their own so that if you clear an area, and then you replant right away, you can at least get a leg up that way. So a lot of them, it won’t actually outcompete by themselves, but maybe together with other ones, they’ll hold the ground from further encroachment, and so…
Margaret: Right. And you’re still weeding. It’s not that you’re not pulling out garlic mustard, for instance, or in some cases, like you said, using a cover like cardboard or something to stifle things. It’s not that you’re not doing that, it’s that you’re not only relying on that.
Nancy: Exactly. And the golden ragwort is pretty unique in that. I did still weed just the first year or two, and then I didn’t have to. It just pretty much does this wonderful takeover. But yeah, some of the other ones, it takes longer to keep weeding out, but it’s less and less each year, and that’s so rewarding.
Margaret: Right, and these are in areas… So describe golden ragwort to us as a plant. What does it look like? What does it do? What’s its… [Packera aurea, above, from Wikimedia; photo by Derek Ramsey.]
Nancy: Packera aurea, and I think obovata also up where you are is native, has roundish leaves that grow densely together. The plants root underground really quickly, but then they also spread by seed. And so it’s a beautiful ground cover all season and often all year. And I love it because the birds love to forage in there, too, and the rabbits make nests in there. And there’s a specialist bee that goes to the flower, which is maybe about a foot tall, and bright yellow, and just lights up the whole place in spring.
And it’s really pretty with plants like phloxes and purple… What is it? Phlox subulata and stolonifera, and the woodland Phlox divaricata. What I started doing with it, too, is planting it under trees. I’ll start there under the redbuds, under the chokeberries. When I do tree cages, when I plant new trees now, I put a lot of groundcovers like that. Or sometimes I’ll even put bigger plants like Rudbeckia in there with the tree cage, as a way to green mulch it instead of mulching it.
Margaret: So right from the start, when you’ve disturbed… In order to plant a tree, you’ve disturbed the soil, you are right away planting some groundcover to be with that new tree.
Margaret: Yeah. So not letting that… Because what does a weed love more than anything? It loves open ground, disturbance. Right? So you’re trying to get ahead of it. Do you have other perennials in the way that the Packera, the golden ragwort, do you have others that you have found have served this kind of role particularly?
Nancy: Yeah. Well, the sedges [Carex], some of the sedges, they don’t grow quite as vigorously, but pretty vigorously, like the blue sedges and the Appalachian sedge. And then I like things like tufted hair grass [Deschampsia cespitosa], which is evergreen, and that really holds the ground against anything. I don’t know if that’s the reason, or if there are other reasons.
Margaret: Well, leaving any blank space at ground level, obviously… If we go and we pull out all our garlic mustard, and we leave a blank canvas [laughter], what’s going to happen? Who knows what’s coming next? More garlic mustard and then who knows what else? So we have to be there. It’s the one-two punch. Right? We have to be there with it. Right, right.
Nancy: Right. So depending on where you are, some of them are such great host plants and pollinator plants, too, like golden Alexander for the black swallowtail and-
Margaret: The Zizia. Is that Zizia?
Nancy: Yeah. Once that gets going, wild basil, wild ginger of course and the shade.
Margaret: I was just going to say the Asarum canadense. I think the wild ginger is one of the great native groundcovers. And it’s, for me, again, even in a very cold zone, and it’s not evergreen, like the European version of Asarum is a more evergreen leaf, but it’s thick, dense, at ground level, controllable. It’s not like it goes crazy and takes over your whole place, but it really makes a great groundcover that not a lot of stuff gets into. So if you have, as you say, under trees or a shrub border or something where you want the ground… You don’t want to have to be weeding 50 times a year in that area. You want a dense groundcover to close the ground and also have some beneficial elements to it, features to it. Yeah. That’s a great one, I think.
Nancy: Yeah. And I remember reading this tip from Barry Glick at Sunshine Farm in West Virginia, about planting wild ginger under pawpaw trees, because they have the same or similar pollinators, flies.
Margaret: Oh, interesting [laughter].
Nancy: So I went down to transplant some under the pawpaws this year because I’ve been meaning to do it for years. And I put the pawpaws as bare roots many years ago, far down in the field, just right into the turfgrass. And over the years there was garlic mustard under there and stiltgrass. And this year when I went to put the ginger, I saw that it’s now almost all violets [above, at Nancy’s]. So that’s another really nice recruitable one you don’t even have to plant. And I guess because the pawpaws shaded out the turf entirely and the other stuff, it’s just all violets now under them.
Margaret: And those are such… And I think a lot of people still even think of them as weeds. And they’re such helpers, and they’re such supporters of all the fritillary butterflies I think use them as host plants. And they’re so charming and tough, but it’s like we have to recondition the way we look. But especially in these, it’s going to be a little looser, a lot looser. But it’s also going to be functioning and supporting to beneficial insects and other animals. And it’s going to hopefully, like we’re talking about, keep out some of the really unwanted things like that mugwort, like that stiltgrass, like the really unmanageable ones that are nonnative and big trouble.
Margaret: So any other perennials that you’ve found that are doing a good job at sort of… Again, I shouldn’t say out-competing, but helping take up space, and keeping things, that have the strength [laughter] to resist some of the other…
Nancy: Well, I love elephant’s foot. Do you have that?
Margaret: I don’t think I know what that common name-
Nancy: Elephantopus carolinianus.
Nancy: And there’s another one, too, related, and well that is a really dense groundcover, too, not all year, but all season. And so it really holds the ground, and it has these little small purple flowers that buckeyes and other little butterflies love in the late season. And that’s good for shade or part shade. I have it even in a fair amount of sun, part sun, too.
And then lyreleaf sage [above, at Nancy’s] is so pretty, and it just goes anywhere. You can’t even walk on it. It won’t flower as tall, but…
Margaret: I don’t think I know that common name, either.
Nancy: That’s Salvia lyrata and-
Margaret: Lyrata, O.K.
Nancy: It has the cutest little leaves. And actually that’s kind of evergreen. It’s sort of ever-purple. It kind of disappears. You can’t really see it very well, but it can keep the leaves all year sometimes.
White wood aster, that tends to get browsed in certain spots, but if it’s protected with other plants around it-
Margaret: Well, the asters, all of them here get browsed, and even the woodchucks and the rabbits love them, for instance, because I don’t have deer; I have a fence. But what I think of it, when I see that happening, instead of getting hysterical, I just think it’s the Chelsea chop. Do you know what I mean?
Nancy: [Laughter.] Right.
Margaret: It’s that pruning technique. It’s being cut back in spring when it’s partway grown. So it’s going to delay flowering a little bit and make it flower slightly shorter size. But the thing I am glad you mentioned as the white wood aster, and really to me, even other native asters. Early in my garden career, I used to pull them out of areas. They would sew in, and I would pull them out because they seemed weedy. I mean, that was my mindset 30-plus years ago. And now I’m thankful that they’re doing that, like the violets. And I think it’s an important… You’re just making me think it’s an important mind shift that we have to do is to make friends with and-
Margaret: …and appreciate. Yeah.
Nancy: That’s totally it.
Margaret: What about northern sea oats [above at Nancy’s with ostrich fern, another native choice]? Have you found that to be a good helper or what’s…
Nancy: I love that. Yeah.
Margaret: Chasmanthium latifolium, the northern sea oats grass.
Nancy: Yeah. And actually, I don’t know about where you are, but here people think oftentimes, “Oh, it’s too aggressive.” But that is something that if you’ve got it with a lot of other natives, and it grows alongside certain ones, or it even protects them, I’ve found. We’ll see what happens over the years. But I’ve had it for quite a while now, and I have some perennials mixed in that do get browsed now, like wild bergamot and even Echinacea and stuff, and they are doing well among the sea oats.
The sea oats also really help with the Japanese stiltgrass. Now I think that some people, it’s very hard to tell the difference until you get to know them when they first come up. The sea oats and the stiltgrass can look pretty similar [laughter].
You just have to do it for a little bit and then you get an eye for it. But that in combination with a native grass, nimblewill [Muhlenbergia schreberi], which I love. It’s just very thin-leaved and a shade grass, and it’s very maligned, too, online by mainstream sources and lawn experts and stuff. But it’s a really good one for holding the ground also against stiltgrass. And so I love those plants. And sea oats is a host plant, too, for some butterflies and moths, yeah.
Margaret: And it does have the most incredible seedheads of anything I’ve ever seen [above, at Margaret’s]. They look like a flattened pine cone or something. It’s like these just incredible… And they kind of take on a coppery color or something in the fall. It really is quite a beautifully constructed architectural little creature.
Nancy: Yeah [laughter]. It really is. And in the wind it makes it pretty sound.
Margaret: Yes. I think when we did a recent “New York Times” story about your “Wildscape” book and so forth together, and I think you mentioned something, blue mistflower. Is that… And you also mentioned false nettles. Tell me about those two. Have those been ones that have been helping you with this battle?
Nancy: So yeah, blue mistflower actually came up in a sneezeweed plant that I bought at a local native nursery here. And so I never intentionally bought it, although I would have eventually, I’m sure. But it looks kind of like hardy ageratum. It’s really beautiful purple fuzzy flowers. And it tends to not be browsed by deer. I think it has some alkaloids in it that they don’t find tasty. So it seeded here from that original pot, and then it eventually went out into the field where the stiltgrass is, and it’s been making ever widening circles in the stiltgrass. It doesn’t seem to mind growing among it at all.
Nancy: Yeah. So I just go and I pull around it, and I do that with the false nettle, too. It does the same thing. And every year if I just pull some more around it, then those things can reseed into the bare spots that I make and keep on spreading.
Margaret: So the false nettle is Boehmeria, I think. And I think the blue mistflower is Conoclinium [above, with Rudbeckia, at Nancy’s].
Nancy: Yes, C. coelestinum. Yes.
Margaret: Coelestinum, yeah. I always had trouble with that one because it has so many vowels in [laughter]. I could never say both the genus and the species have so many…
So if this sounds appealing to people, to adjust how they see some plants like the violets and the asters and leave some of them. And again, letting, or either adding or letting some plants like the false nettles and the blue mistflower and so forth, get going in a patch of something that’s troublesome. And then weeding out the troublesome stuff around it and letting the good thing take more territory.
Besides your book, besides “Wildscape,” are there other places to do homework about this or to learn more about this? Did you use field guides or any other tips in the last couple months? Yeah.
Nancy: So while I was exploring these things, I think Larry Weaner came out with his book “Garden Revolution” [affiliate link] a few years ago, and he talks about this in that book somewhat. And then “Planting in a Post-Wild World,” of course, talks about using natives to hold the ground and such. And so-
Margaret: Thomas Rainer and Claudia West’s book, O.K. Good suggestions. Thank you.
Nancy: And I think one of the things over the years that I’ve just learned is that people get really excited by this topic. I wrote something on my site in like 2016 or something, and the amount of comments on there was incredible compared to other things that I’ve written.
And it’s because people either want to know what’s going to outcompete something or they want to share their experiences. And so I’ve just learned a lot from conversation with other people, too. And I started experimenting with what they told me and including their stuff in my handouts and such. And shrubs and trees are really important to this too, helping to shade things out or the suckering shrubs, because we have a problem with some of the invasive suckering shrubs and so-
Margaret: We’ll have to talk about this again again,because we’ve run out of time. But I so appreciate, Nancy Lawson, your taking time today to join me to go a little deeper into this topic. [Below, a seating area in Nancy’s wildscape.]
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 14th year in March 2023. 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 June 12, 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).