Ironweed’s Beauty and Ecological Value in Your Garden: Mt. Cuba’s Vernonia Trial

Introduction

Sam: There is an iron weed for every garden. And again, I mean, they’re beautiful plants. They have, they attract tons of pollinators, including one specialist bee that we saw in the trial garden, which was a ton of fun to watch. Yeah, it’s just a great group of plants that I hope more and more people will start adding to their home landscapes.

Shannon: Nature isn’t just “out there” in some pristine, far-off location. It’s all around us, including right outside our doors.

Hi, my name is Shannon Trimboli and I help busy homeowners in the eastern U.S. create thriving backyard ecosystems they can enjoy and be proud of.

Welcome to the Backyard Ecology podcast.

In today’s episode we’re talking with Sam Hoadley. Sam is the Manager of Horticultural Research at Mt. Cuba Center where he evaluates native plant species, old and new cultivars, and hybrids in the Trial Garden.

Hi Sam. Welcome back to the podcast.

Sam: Hi, Shannon. Thank you so much for having me back.

Shannon: Oh, you’re welcome. Some of our listeners may remember you because you were on in 2023 to discuss Mt. Cuba’s Carex or sedge trials. That was a really fun episode and a lot of people really enjoyed it. I’m still getting comments about it.

Today we’re going to talk about another group of plants that are also very beautiful. And I’d say they’re much better known than the Carexes or sedges, especially among home gardeners and people wanting to do native plants. So, it’s going to be another fun conversation.

Overview of Mt. Cuba Center

Shannon: But, before we really kick into that group of plants, let’s start at the beginning because some of our listeners may not be familiar with Mt. Cuba and the trial gardens or what you do. So, let’s start off talking a little bit about that and we’ll start at the beginning, the very beginning. Where is Mt. Cuba?

Sam: Sure. Mt. Cuba is located in Northern Delaware, very close to the Pennsylvania border. We are in this tiny little sliver of Piedmont ecoregion in northern Delaware. (It’s much more common just north into the Pennsylvania border.) But a very hilly area. Forested. A very beautiful rural space. And Mt. Cuba Center is a botanic garden focused on native plants and their conservation.

Shannon: Yeah, because a lot of people when they first hear “Mt. Cuba,” they don’t think of Delaware. I mean, I know I didn’t, when I first heard of Mt. Cuba.

Sam: Right. The name comes from… I believe it’s actually derived from an Irish word. There was an Irish settlement in this area, and I can’t remember exactly the word, but it has over the years evolved to be “Cuba.”

So there’s a few places that were named for the little settlement in this area, and there’s a few institutions around here that are named Mt. Cuba Center, or there’s the Mt. Cuba Observatory, but it’s all just kind of descriptive of this small little area in northern Delaware.

Shannon: Oh, nice. I hadn’t heard that part of this story.

Sam: Yeah. I wish I had that Irish name, or word, to really like drive it home, but that is where it originates from.

The trial gardens at Mt. Cuba

Shannon: So you’re focused on native plants and then you do these really awesome trials. Um, can you tell us a little bit about, well, first the trial gardens themselves, and then how are those trials conducted?

Sam: Yeah. To give you even more context, the trials were set up by the previous owners of Mt. Cuba Center. It actually used to be an estate garden and the Copeland family lived here. They moved here in the 1930s and it became important to them to garden with native plants.

They kind of realized their passion was in native plants and open space conservation. And it was really their intention for this, their home, to eventually be open to the public and they wanted to inspire people by the beauty and value of native plants. And that lives on today in our mission and everything we do at Mt. Cuba Center, including what we do in the trial garden.

So, the trial garden was actually the brainchild of Mrs. Copeland and was one of the first places in Mt. Cuba Center to be repurposed. T he trial garden used to be the cut flower garden and, after she passed away in 2001, it was transitioned to a trial space.

Um, and that’s what we do here. We want to inspire people by the beauty of these native plants and all of these species cultivars that we’re growing in the trial garden. But we also want to inspire people by their value. And in the trial garden, we interpret the value as their ability to support wildlife. Most often, we’re looking at insect interactions with the various species and cultivars in the trial garden to try to help people understand which of these plants may be able to best support wildlife in this region, the Mid-Atlantic region specifically. And which plants may just be really well adapted to common garden conditions in this area as well.

Adapting trial results to different regions

Shannon: I love that. I mean, it’s Mid-Atlantic, so it really works well if you’re in that Mid-Atlantic region. Someone, like me, who is in Kentucky – not the Mid-Atlantic – and I know there’s a lot of people from other areas that look at your stuff too. We have to take it with a grain of salt and do a little bit of thinking about, “okay, does this really apply here?” Or how do we tweak it for our area? But it does give a lot of, at least general concepts, broad ideas, things to think about, and pointers for the rest of us too.

Sam: I like to think about the trial results and the trial program as giving people a framework to help them make informed decisions about what may or may not work for them. The region that we’re most likely going to apply most of our results to is the Mid-Atlantic, but we’ve found that our results may have applications to New England, the Midwestern U.S., and southeastern United States.

Um, Richard Hawke at the Chicago Botanic Garden has been doing studies, or trials, there for decades. And it’s really interesting. Even though our trials are not necessarily linked or planned together, when we do trial the same groups of plants, or genera of plants, it’s interesting how frequently a lot of those top performers do kind of cross over both of our trial programs. It’s not true in every case, but a lot of times it does show you that a good plant in one region doesn’t necessarily mean it’s going to be a bad plant in another. A lot of times it actually means a good plant is a good plant.

Of course there are exceptions to that, but there’s also nuance in looking at our trials too. We’re evaluating plants in one soil condition – our average garden soil. It’s a clay loam pH between 6 and 7. We don’t add anything to it. We’re not watering. But some plants are well adapted to that. And even though it’s a very hands off trial program, the plants that are adapted to those conditions
are going to be the plants that are top performers at the end of our trials.

Right plant, right place

Sam: I often talk about species, especially with species heavy trials, but there’s no bad species. It’s just certain species are adapted to that middle of the road, average soils, or are adaptable. Others really want wet soil conditions or dry soil. Dry soil conditions may not perform really well in the trial garden. But if you have wet soils at home, or if you have really dry soils at home, there might be plants in the trial garden that might perform really well for you.

So, we do try to share why those plants may not perform well on the average and try to tell people where you could use those plants and you might have better results with them.

Shannon: Yeah, and that’s one of the things I like about the reports and the trials that you give us because it’s the, “okay, this has worked well in an average soil for our area, but here’s everything else that we tried.”

And so it gives you that ability to, like you said, make those informed decisions and maybe try some of those other plants because while a lot of people have kind of average soil, there’s a lot of people who have “not average” and one extreme or the other.

Sam: Yep. No, it’s really interesting. There are plants in our trial that I feel like… I really enjoy gardening with plants that want drier soil and that sandy, rocky gravelly soil. And those plants that I get really excited about in our trials really struggle in the trial garden.

It’s tough to watch them because, you know, they’re just not in the right situation for them to thrive. But, you think about someone who’s growing in that rocky soil. And I think a lot of times people who have that soil are like, “I wish I had that beautiful clay loam.” And I’m like, “Oh, no. I want what you have.”

So, it’s just interesting that those plants, for us, aren’t the best performers. But maybe just downstate in Southern Delaware where the soils are sandy, or in a coastal plain situation, they might actually be really, really great garden plants.
So we do try to introduce that concept as often as we can in the trials too.

Shannon: Yeah, I mean, there’s a lot of rocky soils down here where I’m at, and I hear people all the time, “Oh, I’ve got these really poor rocky soils. Should I bring in more dirt? Should I do this? Should…?”

And I’m like, “No. Let’s find plants that work in those rockier soils because there are native plants that really do well and thrive there.”

Sam: Yeah. It’s about embracing those conditions. I think plant selection is the first step – researching that plant and understanding it – is really the first step in making sure that your landscape is going to thrive. Hopefully we can give you some of those first steps from our research program.

Shannon: And even if a species that you’re testing and trialing isn’t native to where I’m at, which it’s amazing how many species are native throughout the range, especially ones that you’re going to be trialing because you do a lot of trialing ones that are easier to find.

Sam: Yep.

Shannon: So that by definition kind of narrows the range because people like to grow plants that they can sell in lots of different places. So, that means that they want to grow these plants that have these wide native ranges. So, there’s a lot that work well in lots of places, but even if there is one that isn’t native to where I am, I’ve found a lot of times I can go, “okay, he was talking about this plant, this species. We may not have that one, but our equivalent here would be this.” And I can again, use those as informed choices to kind of give me ideas.

Sam: Right. Hopefully inspire. That’s a whole big piece of this. Yep.

Beauty and ecological value of ironweed

Shannon: So, your most current trial that you just wrapped up and finished the report on are on the Vernonias, which are what we commonly call the ironweeds. They are absolutely gorgeous. I love them.

For anybody that might not be familiar with them, which I think a lot of people are, but those are those deep, rich, dark purple flowers that we commonly see in the mid to late summer out in the fields, the prairies, the meadows, the places that you’ll see goldenrod in a month or two. I love it when the ironweeds and the goldenrods are blooming together. That’s just stunning.

Sam: It’s spectacular.

Shannon: And they’re always covered with so many butterflies and bumblebees and insects and everything else. I just love watching them. It really is a, a magnet for all kinds of wildlife and critters.

Sam: Yeah, it’s one of those groups of plants that have beauty. They have ecological value. I was really excited that we were trialing ironweeds because I feel like many people are familiar with them, but I feel like they’re often underutilized in a landscape situation. And I feel like this trial gave us an opportunity to really shine a light on a really incredible group of plants.

I think people tend to think about ironweeds, at least around us New York ironweed is our most common species in this area, and people associate it with, you know, it grows in wetter areas and like floodplains or even roadside ditches. But there are ironweeds out there from throughout the eastern temperate forest ecoregion, or basically eastern half of the U.S., which is our definition of native in the trial garden that will grow in just about any soil condition.

And just again, it’s about choosing the right species for your place, but there is an ironweed for every garden. And again, I mean, they’re beautiful plants. They attract tons of pollinators, including one specialist bee that we saw in the trial garden which was a ton of fun to watch. Yeah, it’s just a great group of plants that I hope more and more people will start adding to their home landscapes.

Shannon: Yes. And like around here, our most common native species is tall ironweed. We’ve got some New York in Kentucky, but tall ironweed is really the one that you’re going to see the most. And so, yeah, a lot of times it’s easy for me to go, oh yeah, ironweeds and I’m thinking tall ironweed. And you have to really be careful where you put it because it’s called tall ironweed for a reason.

Sam: Right.

Shannon: I mean, it gets TALL sometimes if it really likes where it’s at, but there are other species that work really well in other locations.

Diversity and hybridization of ironweeds

Shannon: There are actually, what – 20-ish different species native to North America, about half of which are native to the eastern US, that eastern temperate woodlands ecoregion area. Correct?

Sam: Yep. There’s a surprising amount of diversity. I mean, for a genus that, again, in our area we’re familiar with one or two locally native species. Tall ironweed does kind of eek into Eastern Pennsylvania, just in a few counties. But yeah, I think when you start going to the southeastern United States and the Gulf Coast, there’s so many interesting plants and the Ozarks, there’s a couple of species there that are really, really cool.

Yeah, again, there’s a surprising amount of diversity in ironweeds, and even worldwide. They’re, I believe, found in most every continent. But our center of diversity is eastern central U.S. There are some species that sneak into the Western U.S. a little bit too.

Shannon: And then if you’re a botanist and out there kind of nerding out in the wild, ironweeds, especially when the species get close together around kind of those boundary lines where the ranges are coming together, they hybridize quite frequently.

Sam: Yep, they can. And we saw that in the trial garden. If you have multiple species in close proximity in cultivation that bloom at the same times, you are very likely going to end up with hybrids.

For a plant breeder, that’s a great opportunity. But if you really want to have a species and you want to keep that species, so that it is the wild type and not have those hybrid or intermediate plants, then it’s important to make sure that if you have multiple species, then you have those bloom times be separate. And there are ways to do that.

We saw some of our ironweeds in the trial garden started as early as June and finished in kind of mid to late July. Other plants didn’t start blooming until mid to late September through October and November. So, there are ways to do that if you really do want the wild type plants to remain that way. But yeah, if you have multiples out there, you’re going to end up with some really interesting intermediates, which can be fun. But again, just be aware that that can happen.

Shannon: That was something else I wanted to make sure we brought up. I know a lot of people, they love ironweeds and they want one of ALL the different species. This is a big consideration if you’re trying to do that with the ironweeds.

Sam: Yep. Now, I know even in my home garden I have Vernonia angustifolia, gigantea, noveboracensis, and we have these funny intermediates that just show up that nobody planted. Neat garden volunteers that you can a lot of times kind of suss out what the parents might be. We still see pollinators on them. But it’s, just something to be aware of again, that it’s very likely.

It’s the same thing with Amsonia. Clematis will do the same thing. When you bring these plants into an artificial setting and cultivation, there’s sometimes some mingling that maybe wouldn’t happen all the time out in nature. But it still does happen out in the wild in certain situations.

Species in the ironweed trial

Shannon: So how many species did you include in the ironweed trials?

Sam: I believe we had 13, but with most of those species we had multiple versions of each of them. In a lot of cases, we tried to have either a wild collected form of that species, and by wild collected I mean wild collected seed that was then grown in the greenhouse, as kind of our baseline or our control. Then sourcing a plant of that same species from a commercial source. We may not know where the origin of that plant was. And then the other, the next layer, would be the cultivars. And most of the cultivars in the Vernonia trial were selections of wild type plants, but there were a few hybrids as well. I think we had four different hybrid ironweeds in the trial. But it was very species heavy.

And there was a lot of concentration on comparing different ecotypes or origins of the same species. One example, we had I think 7 or 8 forms of New York ironweed, a lot that originated from the Mid-Atlantic. We had one selection, which we’re not really sure where it originally came from. And then we had another form from South Carolina. It was very interesting seeing how differently the plants, especially from South Carolina behaved, in comparison to our Mid-Atlantic ecotype in the trial garden.

Importance of ecoregions and ecotypes

Shannon: Yeah, that would be interesting to really dig into. And it shows how different, like you said, the ecotypes can be and why it’s important to, if you’re trying to keep it more natural in your garden, to pick those sources that are closer to you whenever possible.

Sam: Yeah, regionally appropriate, or where that plant came from in the wilds, if that’s your goal, can make a big difference in the plant’s behavior. So for example, New York ironweed in this region tends to grow to about 6 to 7 feet tall. If it’s really happy, maybe up to 8 feet. And blooms in August or early September.

We found in the trial garden that our Mid-Atlantic ecotype forms of New York ironweed really struggled because they really do want that cool, moist root zone. We’re not telling you don’t plant that plant, but if you have drier or more average garden soils then there are better options that are more adaptable. But if you have wet soils, then New York Ironweed is a wonderful plant. I love growing it at home.

But it’s very interesting seeing that form from South Carolina that was grown right next to those plants. It grew taller. It bloomed about a month later. And it didn’t seem to have any of the issues with the drought intolerance or stress that was associated with lack of water or disease pressures. Which again, those diseases are exploiting a stressed plant that is likely just coming from a mismatch of soil conditions or cultural conditions in the garden to what that plant would prefer in the wild. It’s the same species, but behaving quite differently depending on where it’s sourced from in the range.

What colors of ironweed flowers were included in the trial?

Shannon: So, on the plants that you chose, were they all purple flowered ones? Because we all think ironweeds and purple flowers, and that’s what ironweeds tend to mostly be, but you can have white flowered ironweeds too. I’ve got a patch that’s always white that grows in our backyard. They were wild ones that kind of came in and I was like, “Oh, I kind of like that. We’re just going to leave them there.” So, we mow around them every year.

Sam: That’s really cool. And that can happen. There’s natural mutations where you have maybe a lack of pigmentation or sometimes darker pigmentation. Most ironweeds though, most species and even hybrids or cultivars, are that kind of beautiful dark purple. It’s just a spectacular color that actually the camera really struggles to capture.

But there are white selections out there. There’s one called White Lightning that Jelitto sells. It’s actually a seed strain. It has pretty reliably white flowering seedlings. But we found that that plant just wasn’t overly vigorous. I think that if you have, for example, a really vigorous white flowering form of ironweed out there, then there is commercial potential. There’s always people out there who are interested in kind of the unique or kind of boutique items that maybe wouldn’t fit in every home garden. But it certainly is interesting.

You don’t see it that often, but it’s pretty cool when those mutations are found or just seen in the wild. We’ve heard about some populations that have slightly more pink flowering forms. Someone recently in this area found a chartreuse foliage form of New York ironweed. So, very different and unique. Maybe not to everyone’s taste, but there are these kind of interesting aberrant forms that do occur out there in the wild.

Shannon: I was thinking that they were all purple. Even the cultivars that you guys tried, which makes sense because otherwise you’re getting too many variables out there to compare to each other.

Sam: Yeah But by far 44 of the 45 did have purple flowers.

Selecting and sourcing plants for the trial

Shannon: Why did you choose the species? How do you pick which ones you’re going to get? Or even beyond just which species, where are you going to get them from? Because like you said, you were doing ecoregions as well.

Sam: So, when we’re planning a trial from, I would say from concept to completion, it’s actually like almost an 8 year process, sometimes 9 years. The first 3, 4 years of that are concept, gathering plant material, growing out those plants. If we collected seed, or purchased seed, getting them to a size that might be very similar to what we would buy in a nursery. And then planting all those plants together to start that trial.

It’s kind of a complex system, but generally when we’ve selected a trial, and we go about that through many different ways, maybe we’re trying to promote a group of plants that we’re really passionate about and we feel like need that spokesperson maybe. I think ironweed falls into that category.

Others we’re just looking, basically doing a market analysis. So, I use coneflowers as an example of that. There’s just so many options out there. As a consumer, where do you start? Are these plants all the same? Especially from a pollinator perspective. Are they going to be long lived? There’s a lot of information kind of lacking, especially comparing all these plants to each other. So with some cases we’re just telling people like, “these are the better ones to buy.”

With ironweeds, and same with Carex, it was more about, “Hey, these things exist. They’re great. There’s potential for some of these other species in cultivation that should be commercially available.”

So, when we’ve decided on the trial, once we decide on ironweed, we kind of look at the nursery world, especially in the eastern United States. And we basically generate a list of what we could purchase. So, out of all of these different species and cultivars, what’s out there. Then we use resources like Bonap (The Biota of North America Program), NatureServe, and the USDA website. Then we look at the species lists of what species are native to the eastern temperate forest region that might not be commercially available. And we try to figure out if any of those plants may have commercial potential or are easy enough to source. Maybe we’ll go out and collect seed or work with partners throughout the eastern United States to collect seed for us, send it to Mt. Cuba Center and we’ll grow it.

To me, that is probably one of the most exciting pieces of some of these trials that are very species heavy. Some of these species may not be in cultivation, are rarely cultivated, or maybe not cultivated ever to my knowledge. And getting to know these plants and understand them, it’s a really interesting and unique learning opportunity.

But between those plants that are commercially available and sourced from wild seed, that’s basically how we accumulate all these plants together. And again, recently there’s been a lot of focus in our trials on looking at local ecotype of species, like even Delaware native compared to a form of the species that’s out there in cultivation. Maybe we don’t know where exactly that seed came from. And then also looking at the cultivar question, or cultivars that may exist to that species, and having almost those three layers of comparison, which is fascinating how sometimes they’re very similar in performance and sometimes they’re very, very different.

So it’s really fun to see that in action and have them rowed out next to each other. Those differences, those similarities, really pop out.

Shannon: Yeah, I really enjoyed seeing that on this one because I don’t think you did that on Carex, but not as many people were growing Carexes at the time. But yeah, I really enjoyed being able to see that and really do that comparison

Top performers in the ironweed trials

Shannon: So, which were some of the ones that really stood out in your mind for your Mid-Atlantic average soil?

Sam: Yeah, there were a few. The one that I would say turned the most heads in the trial garden were the giant ironweeds, the Vernonia giganteas, which you would be very familiar with in your part of the world. But oh my gosh, they’re incredible plants. Some of them are tremendously tall.

Most of our ecotype came from the southeastern United States. We had two collections from Alabama. We had a selection, I believe, from the Carolinas, and another selection from Arkansas and they generally bloomed pretty late. I know the Midwestern and the Mideastern ecotypes, especially of giant ironweed, tend to bloom a little bit earlier. So, like that August window into September. But a lot of these southern forms of giant ironweed were blooming September, October. And we had one that was going into November, which was kind of fascinating to see blooms that late.

It actually coincided perfectly with our migrating monarchs. That was like the gas station for the monarchs, if you will. They would just collect there. We actually do monarch tagging and monitoring here at Mt. Cuba Center and we learned pretty quickly that instead of running around the gardens and the natural lands looking for monarchs, we would just wait at the giant ironweeds and they would come to us.

But we found that that species, just in general, was very adaptable to the average garden soils. It didn’t have any signs of stress from lack of water, had no disease pressures, and was just absolutely spectacular. And the profusion of flowers it produces… and, you know, healthy plants are going to be able to attract and support more insects just because they’re offering more value. Yeah, that was just an incredible plan.

That and one selection out there, you may have heard of it from Arkansas. It’s called Jonesborough Giant. Plant Delight selected this a few years ago, I think, back in the two thousands. But that plant is the largest herbaceous perennial I know of. It reached a height of 15 and a half feet in 2022. It was just… I mean, you could see it from across the gardens and everyone that went into the trial garden, whether you were a beginner, maybe were not really familiar with native plants or the whole movement up to like expert gardeners, everyone would be kind of stopped in their tracks by this plant. It was just unbelievable. And, surprisingly sturdy for a 15 and a half foot plant. That was one of our favorites.

There was another selection, actually another selection by Plant Delights, called Vernonia angustifolia Plum Peachy, which is actually a selection of a plant that they found in Georgia growing in pretty dry soils. But it really makes this beautiful mounding plant with relatively fine foliage that’s blushed with kind of this wine colored hue to the stems and the leaves. It has this, again, beautiful shrub like form and incredible flower display, but my favorite piece of it was actually the seed heads as they ripen. The pappus has this kind of coppery, kind of peachy, purpley color. That same kind of hue that’s in the leaves and in the stems. And we found that that plant was really adaptable to average garden soils.

Vernonia angustifolia in general grows in drier habitats, kind of sandier, hot dry. They really don’t like the winter wet in the Mid-Atlantic region. If you want to grow that species, you can, but the trial garden soils were just a complete mismatch for what that plant wants to grow in. And we actually had three other accessions of Vernonia angustifolia, and we have five plants of each accession. Only a single plant of those other three accessions survived. So, one out of 15 survived from those other three. But for Plum Peachy, all five of the ones we planted survived and looked spectacular at the end of the trial.

And then one more. They’re all great. I kind of have a hard time picking my favorites. Um, but another type of form that I really like that is fairly commercially available is Vernonia lettermannii. And there’s a selection out there called, Iron butterfly. Vernonia lettermannii is typically found in the Ozark region in kind of these cobble bars in riparian corridors. It has this beautiful fine textured foliage, which looks a lot like Amsonia hubrichtii. It has that lower mounding form.

If you grow it in drier soils, full sun, it’s going to be completely happy. If you grow it too rich, it tends to spray open a little bit. But that plant, I think it’s one of those plants, we just want to treat it too well in the garden. But if you just plant it correctly, you put it in some drier soils, it’s an absolutely spectacular plant. And another smaller plant so that if you don’t have a ton of room, there are some smaller ironweed options for you if you don’t have the space to accommodate, say, like a 12 or a 15 foot ironweed. But they’re all great. I wish I could plant every single one of them.

Shannon: Yeah, that’s one of the problems I hear… well, concerns, we’ll say, not really problems, but concerns from a lot of home gardeners around me is that gigantea, tall ironweed, is our primary native species here, and not everybody has space for a 10 to 12 foot tall plant growing like that. So it does raise concerns.

Management techniques: Effects of the Chelsea Chop on ironweeds

Shannon: And that was one of the things that I also really liked about this trial and the report, was that you also looked at management techniques and cutting back. Because that’s one of the things that I tell people a lot of times with a lot of different species, especially the asters, is if they’re getting too tall just give them a little artificial deer browsing.

Just cut them back a little bit. Don’t worry about timing. Don’t worry about anything like that. Deer don’t care what angle they’re eating it at or what time of the year it is. They’re just going to go munch. So, just pretend like you’re a deer and snip it off a little bit.

And you guys did some testing of that with the ironweeds too, didn’t you?

Sam: We did. We did it in late May, early June, which is, typically that kind of cutback of those actively growing stems called the Chelsea Chop. That timing coincides with the Chelsea Flower Show, which is where the name comes from. But we did that with a lot of the ironweeds to see if we could reduce the size of some of these really tall species and see what would happen if we cut back some of these lower, more mounding plants and see if there were any kind of overlying or underlying trends with this treatment.

We do this a lot in Mt. Cuba Center with our asters, just like you were saying. There are a few ironweeds that I would absolutely recommend doing this with, especially some of the lower growing plants that have finer leaves. They really respond well to that treatment. You end up with a slightly shorter plant, much tighter in form, much more resistant to that opening or splaying in the middle, which is pretty typical of Iron Butterfly, Vernonia lettermanii.

There’s really two options to fix that flopping. Either plant it in dry soils or do the Chelsea chop. If you do either, you’re going to end up with a really great plant. Even plants like Plum Peachy, Vernonia angustifolia, handled that treatment really well.

We did not see a great reaction from the taller species like Vernonia gigantea, Vernonia noveboracensis, missurica, baldwinii – a lot of these really tall kind of vase shaped plants. They would break buds and kind of develop a lower, more shrubby habit, if you will. But often the union of those new growths to the old stems was pretty weak. Especially once they started to develop flowers and get a little bit of weight to them, if we went through a storm and those inflorescences got wet and there was a little bit of wind, often those new growths would kind of break right at that union. So, it’s probably, for some of those taller species, not the best option.

Although you can go that route, you might have to do a little bit more staking. But, especially for those smaller plants, it can really make a very tight, tidy, little mounded plant.

Importance of bloom time for specialist pollinators

Sam: One thing you do have to kind of consider when you’re doing this is often that cutback, or I’d say almost always that cutback, is going to result in a delayed bloom period. Now it may just be a week, it might be a couple of weeks, but there might be a difference in the timing of those flowers and what insects might be able to access them.

We saw that timing of those blooms to be a very important factor for a specialist bee that we observed. So, by cutting back some of those plants, you may be actually delaying a flower to a point where that plant’s no longer accessible to that specialist pollinator. There’s going to be plenty of other insects that you’ll see on those plants. But yeah, I would just say that’s a consideration to have.

But you’re right, as far as timing is concerned of cutting these plants back, ironweed are very adaptable. There’s fields near us where there are ironweed present. And those fields are hayed, even in kind of late summer. It would be hard to imagine that plant being able to recover and to bloom after it was mowed to, you know, six or eight inches from the ground. But they do. They pop right back up. They’re going to be tiny little plants, but they do flower. It’s just significantly later than they typically would.

Shannon: Right. And I’m glad you brought that up too because that is definitely a consideration when we’re trying to do more than just “plant for pretty flowers.”

When we’re trying to plant for creating these backyard ecosystems and this pollinator and wildlife habitat, we have to also take into account what’s using it and when. And like you said, the specialist bee for ironweed, denticulate longhorn bee, is that the right one?

Sam: Yep.

Shannon: They’re not active necessarily for the whole entire time that ironweed is blooming. They’ve got a small window. So, you’ve got to keep the blooms in that window if you’re trying to help that particular species of bee, or any of the other specialists that might be with any other species, besides just ironweeds.

Sam: Yeah. These specialists have a window to complete their lifecycle basically, or complete that stage of their lifecycle. And we found, at least with the ironweed in the trial garden, these Melissodes bee, the bees that we were counting separately, were active exactly when our locally native species of ironweed were blooming. Which, I mean, that makes all the sense in the world.

Ironweed performance in natural habitats vs. trial gardens

Sam: The interesting thing was that these locally native species, Vernonia noveboracensis and Vernonia glauca, they just struggled in the trial garden. It was, again, a mismatch of cultural conditions for these plants. And because of that struggle, they had issues with disease and with habit. They didn’t produce as many flowers. We just didn’t count that many bees there.

But if you went out to our natural lands where there’s stands of New York ironweed just growing there, naturally, most of them were not planted, at least by us. You saw tons and tons of Melissodes there on healthy plants because they were growing where they want to grow. They were correctly sited. It’s just very interesting seeing that again, a healthy plant’s going to be able to support more insects. So, siting that plant correctly is a huge first step to ending up with a healthy, thriving ecosystem, even in your backyard.

What we found in the trial garden is even though those New York ironweeds were not blooming well and not supporting a lot of insect activity during that month of August and early September, there were other species of ironweed that are not locally native to us, but very adaptable to the average garden soil. So, Vernonia baldwinii was a great example of that. More western species, Midwestern, even into eastern Colorado, that just could handle those drier conditions in the trial garden. They really put on a great flower show just again because they were robust enough and were getting what they needed with our limited care. And they were able to support lots of Melissodes bees.

If we wanted to see Melissodes, we knew that the Vernonia baldwinii was where we should spend most of our time. Because they bloomed during that same time period and they were just more adaptable to our garden conditions. So, it was just interesting.

It was one of those kind of zoomed in views of that whole question of whether cultivars are better than straight species or vice versa. Do cultivars have value? Does locally native matter? And it was just very interesting to have like 45 options for this specialist ironweed bee, that we know really only has one or two options without people bringing in plants from other parts of the country. But seeing that ironweeds were able to support them from other parts of, you know, the eastern U.S., was very interesting. But again, timing was very, very important for that bee.

Shannon: And it kind of makes sense too, to me, thinking about that those other species from other areas would support that bee because it has a pretty wide range throughout the eastern U.S. So, it’s using those other ironweed species in other places. So yeah, it would make sense that the timing of the bloom and the health of the plant would be the two big factors there.

Sam: Yeah, and I think that finding that timing’s really important can even inform natural lands managers. So, if you have like a field with ironweed – whatever the species, wherever part of the country you’re from – if you are haying that field or cutting those plants back prior to their blooms, you’re likely delaying those blooms. Those plants are going to reflush. They’re going to rebloom if they possibly can. But it may have delayed that resource to a point where it’s then inaccessible to that specialist.

So, I think one of our treatments is to kind of have a mixed approach to even a field. So, leaving up a stand of that New York ironweed, making sure there’s some resource there. Not mowing everything a hundred percent; not treating everything all the exact same way. I think can be a really good strategy to make sure there’s some resources that are kind of following that same natural.

Shannon: I’ve heard that often recommended, especially like for mowing in the fall or burning in the fall. Is to have that mixed age group habitat and apply a treatment to a different piece of the land each time. So yeah, it’s a really good thing to think about and knowing that it doesn’t just apply to after everything’s over for the season, but also during the season as well.

Sam: Right, right. Exactly.

Disease and pest pressures on ironweeds

Shannon: And another thing I found really interesting and really enjoyed reading about in this report was you actually looked at the health of the plant and some of the diseases that they get and how that, not just impacted how it looked, but also impacted how the insects were using the plant. I thought that was a very interesting piece to be added in there too.

Sam: Yeah. So we had a couple diseases that really took a toll on some of the plants in the trial garden. It was really a powdery mildew and rust. And this really showed up in a big way, kind of late summer, and impacted some species kind of disproportionately.

Again, a lot of the times it was species that were just not well adapted to the soil conditions. These plants were stressed and the diseases were able to capitalize on that stress. But again, if the plant hasn’t bloomed at that point and it’s getting and it’s getting a disease infection that’s unsustainable, then it won’t flower well and it won’t support a lot of insects.

But there is other side of it too. There’s a species called Vernonia fasciculata, which is native to more of the Midwestern U.S. that grows in similar habitats to where New York ironweed grows for us, kind of in these wetter habitats. And it’s another one that didn’t turn out to be terribly well adapted to the average garden soils. But because it bloomed so early it’s completed that stage of its lifecycle and was able to support tons and tons of pollinators before the powdery mildew and the rust started to have a major impact on that plant’s health. So, it basically completed that part of its lifecycle.

That wasn’t true for most of the ironweeds out there that started blooming in, you know, late July, September, or October. By the time that those plants were blooming or trying to bloom, some of those species, like New York ironweed, had just unsustainable levels of disease, which we see a lot in the trial garden. If there’s going to be a disease pressure, we’re going to see it in the trial garden. There’s just so many plants there that are similar and they’re in close proximity. They’re all susceptible to similar diseases, but that can almost be a good thing.

It can really. When the plant is resistant to disease in the trial garden, we know that that plant in a cultivated setting where it’s not surrounded by very similar plants is going to behave very differently and likely have very, very little disease pressures. Again, if you’re siting that plant correctly, that first step – right plant, right place.

But like Vernonia gigantea, Vernonia lettermannii, Vernonia angustifolia Plum Peachy, no disease issues at all. It was really incredible to watch like Vernonia fasciculata right next to Vernonia gigantea just like covered in white powdery mildew and rust, and the plant right next to it was perfectly healthy. Really no issues, but I’m sure you know, the tables might be turned if the soils were really wet and moist in the trial garden. The performance of that plant might be healthier and more robust, able to resist those diseases much more. It’s very fascinating to see that.

We only had really one pest pressure, if you will, in the trial guard, and that was Japanese beetles, but they only showed up on Jonesboro Giant, Vernonia gigantea. They only fed on the very tips of the newest growth, and then they disappeared and that kind of cleared up and that was the only issue.

Caterpillars and other wildlife interactions

Sam: We had caterpillars feeding on the foliage. We had ironweed curculio weevil. But, we don’t consider those to be pests. Those are native insects that we think of as a bonus to see them utilizing those plants in other ways.

Of course, we are able to measure or look at the pollinator and insect interactions with these flowers of these various species and cultivars, but it’s always really exciting to see wildlife utilizing the trial garden plants in other ways. As a host plant. As habitat. Those are the interactions I think that are really fun to observe.

Shannon: Oh, yes. And of course, I mean, with those caterpillars, not only are you getting the butterflies and the moths that they’re going to turn into, but you’re also attracting birds because that’s the baby food. And so want to have it all there.

Sam: Yep. Well, a fun story actually with those giant ironweeds. The ironweed curcula weevil will essentially lay its eggs in a trench that it will make in the side of the stem. The larva of that beetle will kind of bore their way down through the pith of the stems. Really, we saw very little impact on the plant’s health at all, and they really just impacted the tallest species. Or they were present in the tallest species.

But we would see woodpeckers landing on the stems of the giant ironweeds and going in after those little grubs. And the ironweeds were able to handle that kind of really invasive feeding from the woodpeckers. Again, it was just one of those really cool interactions that was unexpected, but we saw it again and again and again.

It was just one of those fascinating experiences in the trial garden. I would’ve never guessed we would see woodpeckers landing on the stem of a perennial and getting something out of it. It was incredible.

Shannon: Yeah, those downing woodpeckers, it’s amazing what they will go after and how many of those tall plants that they’ll go after and find those little, little critters. And I’ve seen them doing that in a couple of different species.

Sam: Yep. That was a lot of fun.

Shannon: So, what were some of the caterpillars, do you remember off the top of your head, that you were watching use the ironweed?

Sam: There was Spilosoma, the yellow wooly bear. That was most of the ones that we saw. There were many different color, uh, like forms or morphs, if you will. We had ones that were really kind of white to yellow to caramel colored. That was the species we saw quite a lot of.

We did see some of the flower feeding caterpillars, the ones that will kind of tack the floral parts to their backs to camouflage themselves. We saw a few of those.

We didn’t actually see this caterpillar in the trial garden, but adults of this moth have been picked up in moths surveys of our natural areas. This was the ironweed borer moth, which we were kind of hoping we would see in the trial ground, but we didn’t get to see them.

It just again shows you how much these plants are really doing to support wildlife, even in a cultivated setting. Those yellow woolly bears found the trial garden. Those Melissodes found the trial garden really quickly. We saw them year 1 and year 2, and they were supporting these insects with relatively complex life cycles. It just goes to show me that it can apply to a home garden, even if it’s a smaller home garden. You can support those life cycles as well in similar ways.

Shannon: Yeah, and I mean, like you at the beginning, the monarchs were loving it when they were coming through. We see quite a few monarchs on ours too.

Sam: Yeah, it seems to be a favorite. And, I know there’s a lot of focus on milkweeds, and rightly so, but thinking about plants that can support those migrating adult monarchs is important too. And giant ironweed seems to be one of those perfect candidates for us. They were maybe not always there, but it was a very, very popular plant with them.

Shannon: American Bumblebee is another one that I often see on our tall ironweed in the fall. If I’m going to find them, that’s where I go to look for them at, is the ironweeds. I mean, it just seems like that’s always where they’re at.

Sam: Yep. Then we would see a lot of skipper butterflies – silver spotted skippers, a lot of the, you know, the smaller brown skippers that I can’t identify, but there was dozens or hundreds of them sometimes on a single plant at any given time. It seemed that there would be just these hatches, if you will, of the skippers, and they would just be everywhere. Especially during that kind of that late summer and fall transition, there’s a lot of activity. Generalist pollinators, specialists – ironweed has a lot going on for it in terms of ecological value.

How to look for the specialist Melissodes bee

Shannon: Yeah, and I’m going to make sure I get out more this fall and look for those specialist bees because I don’t know if I’ve never seen them, but I’ve never recognized them or paid attention to them if I have. I mean, there’s always bees on the ironweed, but to actually look and say, “Oh, wait a minute, that’s that one. That’s the specialist bee.” I haven’t done that yet.

Sam: Yeah, they’re really fun. They’re very charismatic. And to just give people an idea of what they’re looking for the females are the easiest to key in on because they’re collecting the ironweed pollen, which is bright white. It almost looks like a bleached flour. It really grabs you visually.

Even though it’s a small bee, it’s maybe half the size of a honey bee. Focusing in on those hind legs that are packed with that white pollen is a really great way to see them, even when they’re moving pretty quickly. They’re black and white and they move pretty quickly. Males even more so. They’re very erratic in their movement. They’re just drinking nectar and looking for females. But you can really watch those females. They’re just methodically going flower to flower, collecting that pollen, which they’ll bring back to their ground nest to provision their larva with. They’re very cool. They’re a lot of fun to watch.

We didn’t know they were there. I didn’t recognize them until we had an entomologist on site who said, “Oh, we’ve got Melissodes here.” And we were like, “Oh, yeah, that’s really cool.” Then we decided that we have this opportunity to count them. We felt like we got to know them and understand like, “Oh, they’re getting out of bed a little late today. They’re showing up a little later.” Or “This is a big day for the Melissodes,” or “not so much.” And you started to learn their favorites. They’re a lot of fun to watch.

And knowing how to recognize them, you see them at home. You’d see them out on walks. They’re around. They’re a pretty common bee. If you have ironweeds in your home garden or out in natural areas around you, just take a look and look for those little white packs of pollen on those hind legs of those bees. You’ll probably see them.

Shannon: I was thinking the males would’ve been easier because of the long antenna, the long horns.

Sam: Yeah, which is where they get their name from. The females have relatively short antenna. But the males are just…they’re very fast, very difficult to photograph. It was one of those that we really wanted to get a good photo of them for the report, and they were giving us a heck of a time trying to get a good image of them. The females, again, they’d spend a little more time on flowers. They were easier to get in and get a close picture of.

I would say, a pretty small proportion of the Melissodes that we saw was male. It was maybe… I tend to say like one out of every dozen Melissodes that we saw was a male and the majority of the insects that were counted were females. That’s just because we simply saw more of them. We were counting both. Again, totally fun to watch. They’re really a really cool native bee.

Upcoming trials

Shannon: Yes. It sounds like it is. Let’s see, is there anything else that you think we should talk about here?

Sam: There’s always new things going on in the trial garden. If you are able to come, or if you’re in the area, we open April 1st. We close around Thanksgiving. But the trial garden, there’s always something new to see. We try to have something in spring, summer and fall.

This spring we have our Tiarella trial. We have ferns, which are going into their third year of their evaluation, which is a lot of fun. We’re not really seeing pollinator interactions, but we are still seeing wildlife utilizing the ferns. It’s, really fascinating. Even some caterpillars that kind of do that tying of the leaves and make those little fern balls. They’ll feed on the foliage within. The fern trial’s really fascinating.

Then in the summer we’ve got a new Pycnanthemum trial, which if you’re looking for pollinator interaction, that is the place to be. We have Physostegia, which we’ve seen a lot of interesting insects on and other pollinators including hummingbirds. We have an oak leaf hydrangea trial, which is kind of our second part to our general hydrangea evaluation. We looked at wild hydrangeas. Now we have the oak leafs.

We also have a milkweed trial. We’re really kind of focusing in on the monarch aspect, which, I mean, you may have guessed that. But, we have 25 commercially available milkweeds and are trying to understand which of these plants in cultivation these monarchs are maybe favoring or utilizing more. So, again, if you have a small home garden, it may be just helping you choose which milkweed will give you the best chance of supporting monarchs in your home landscape.

But yeah, lots going on. I’m sure I’m forgetting something. We’re actually going to be planting a new trial this spring on what we’re calling the bluestems. So Schizachyrium, Andropogon, a lot of cultivars, but a lot of species. We did a lot of collecting locally, even in Delaware, to try to showcase the incredible diversity that exists in these two incredible genera of grasses. So again, lots going on and always something to see.

Coming up next year we’ll be talking about a new publication on goldenrods, which I’m really excited about. So that was a trial we did that looked at 70 different goldenrods. And again, another group that is just incredible at supporting wildlife, pollinators, and other insects. We saw several different species of caterpillars feeding on the foliage. We saw warblers utilizing those plants during their migration, picking off all the little insects that were present on the plants and in the flowers. It’s just another trial that I get excited about. But they’re all a lot of fun. Always something to see and to check out in the trial garden.

Shannon: Oh, yes. I mean, you’ve got a bunch there that I’m like, “Oh, we got to have you back for this one, this one, this one, this one.” There’s so many here, because I mean, goldenrods and the milkweeds of course, because, well, they’re milkweeds, just have to do that one. But goldenrods are another one of my favorites. Always have been. Ferns are one that everybody’s always asking about, especially for shade gardens and stuff. Oh, and the Pycnanthemums, the mountain mints!

Sam: They’re incredible! From a pollinator aspect, just from an insect activity aspect, it’s a little overwhelming. And, you know, I’ve been joking a lot about like how we’re possibly going to count all of these pollinators.

We are very lucky to have a robust pollinator team called the Pollinator Watch team who is observing these plants and counting these pollinators. And just like, how are we even going to do this with the Pycnanthemums? There’s just so much activity. There’s so much diversity. I mean, it’s a great problem to have, but we’re going to have to get creative, I think.

Shannon: Yeah, definitely. I bet. Because like you said, they’re just amazing. And if you want to see really cool wasps in the summer, you go for the Pycnanthemums.

Sam: Yep. No, it’s amazing. I feel like every time I’m out there I see a species of wasp that I don’t think I’ve ever seen before. There’s a blue wing wasp, it is a pretty common wasp in our area. It actually parasitizes Japanese beetle larvae, and there was a week when all of a sudden there must have been a hatch of blue wing wasps and there were thousands of them on the Pycnanthemum.

It was an experience and it was a really cool way to get people up close to these insects. And, you know, people sometimes have a little bit of a phobia about bees and wasps, but getting people comfortable and realizing those bees are, they’re interested in one thing, they’re not going to bother you. I think it’s kind of an exposure therapy, I guess, of bees and wasps.

Shannon: And it’s not just the flowers that are providing so much for them, because when I go out and I’m cutting things back in the spring… I’ll start cutting back usually about the time the red buds bloom, especially the mountain mints, the Pycnanthemum, because there’s this little bitty, teeny tiny gnat sized, I’m assuming it’s a bee but it could be one of the gnat sized wasps, that just absolutely as soon as I cut those stems back, they’re in them. There’ll be like maybe a week where it’s just a flurry of activity and then nothing. And so, I mean, even in those, what we think of as the off season, they’re still doing a lot.

Sam: Absolutely. Yeah. And we see those same camouflaging caterpillars on the Pycnanthemum, those caterpillars that are attaching floral parts and bits of leaves to try to hide themselves. It takes a minute to recognize them, but I mean, they’re out there too. And there’s a spinx moth that specializes in Pycnanthemum. We haven’t seen that yet, but, you know, fingers crossed.

Again, these kind of hubs of ecological activity. It’s hard to go wrong with Pycnanthemum and goldenrods and ironweeds. Like they’re just these powerhouses that you can include in your home landscape.

Shannon: And they’re gorgeous too. So, if you’re going for pretty, these are beautiful in and of themselves.

Sam: That’s right.

Shannon: So, we’re just going to have to have you again.

Sam: Yes. Exactly.

Resources

Shannon: But yes, thank you so much for being a guest on the podcast again, and for sharing the results of the Vernonia trials with us. And for all of our listeners, I’ll have a link in the show notes to the research report so you can find it very easily as well as for the other trials that Mt. Cuba’s conducted.

Sam: Well, thanks again for having me and I look forward to being back soon.

Shannon: And I invite any of our listeners living in the eastern U.S. who are interested in gaining ongoing, personalized coaching and support as you create your own thriving backyard ecosystems to check out the Backyard Ecology Community. You can learn more at backyardecology.net/community.

As always, I want to thank our Patrons and other financial supporters who go above and beyond to help us produce free content focused on creating thriving backyard ecosystems that you can enjoy and be proud of.