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My very unofficial results with my Amsonia would not surprise today’s guest, Sam Hoadley of Mt. Cuba Native Plant Center in Delaware, whose trial garden team there just completed a 10-year evaluation of a range of bluestars.
Twenty different Amsonia were studied over a just-completed trial at the renowned native plant garden and research facility, where Sam is manager of horticultural research. He joined me to report on the findings, and talk about how we can incorporate bluestars into our gardens.
Read along as you listen to the March 4, 2024 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 (and browse my archive of podcasts here).
Margaret Roach: Hi, Sam. Longer days, longer days. Waiting for spring, waiting for spring.
Sam Hoadley: Yes. Absolutely, yes.
Margaret: Oh, my. So like what I said in the introduction, I don’t think I’ve had a perennial with me as long as this Amsonia—it’s a tabernaemontana—that literally just performs. It has never said a thing, has never said, “Margaret, I need this,” or, “Margaret, I need that.” It just performs [laughter].
Sam: Yep. Yeah, they’re wonderful plants. They don’t ask for much and they just give so much year after year, and arguably get better and better. We saw that for a decade in the trial garden, and I’m sure that they would continue to go on for another decade if we were to let them stay in that space. But unfortunately we need to bring in the next trial.
Margaret: Right, right.
Sam: But it was overwhelmingly a high-performing trial. Very few plants had any issues throughout the duration. And in most of our trials, we’re kind of promoting the best of the best, maybe a smaller selection of maybe the top 10 or top dozen or so. With the Amsonia we trialed 20 and all 20 we’re pretty good. And it’s more about how you use them, rather than making a decision on rating. Maybe you’re making a decision on what foliage texture you want, how big of a plant you have space for, those kinds of considerations.
Margaret: Yeah. One fun Amsonia fact that people may not know is they’re related to milkweed, huh?
Sam: They are, yeah. They’re in the Apocynaceae family, so they’re related to the milkweeds. They’re also related to Vinca. And when you look at the flowers and you look at your vinca groundcover flowers, they are remarkably similar, especially with plants like Amsonia ‘Blue Ice,’ those similarities become very apparent.
But yeah, they’re closely related. One of the good cues that you can look for is that milky, kind of latex-y sap, that is quite poisonous and actually is a good deterrent for mammalian herbivory in particular.
Margaret: That means that Bambi and his friends are not as interested in Amsonia probably as in some of the other perennials in your border, yeah?
Sam: Yes, absolutely. Deer resistance is a spectrum, and deer are sometimes hungrier in some places than others, but deer will generally leave Amsonia alone. I have some experience in my home landscape with Amsonia in a highly trafficked deer area, and only on one occasion had they ever been sampled, and it was a very small sample, and then never again. So they are really, really great deer-resistant plants, if that’s a major pressure and concern for you.
Margaret: Yeah, that latex sap of that family, of the dogbane family, doesn’t taste good, I don’t think [laughter].
Sam: Yes, I would imagine not.
Margaret: Nasty.
Sam: I haven’t tried myself, but…
Margaret: No, no, no, no.
Sam: That’s right.
Margaret: Don’t, don’t, don’t.
Sam: That’s right.
Margaret: So this is a genus, Amsonia, the bluestars, that is mostly based in North America and the United States-ish.
Sam: That’s correct, yep.
Margaret: Yeah. So I looked at range maps for all the Amsonia species in the United States. And it’s interesting because though there are quite a number, there’s none in the Pacific Northwest for instance, I think.
Sam: Right.
Margaret: And there’s one, tomentosa I think, in Southern California and some of the Desert Southwest.
Sam: Right. Yes.
Margaret: But generally speaking, they’re Southeast, South and then some in the Central Midwest-ish. I don’t know. You can explain, but who did you look at and where do those come from? Where are they native? Because “native” doesn’t mean native to everywhere in the United States.
Sam: Right, exactly. The definition of “native,” at least what we’re looking at in the trial garden and at Mt. Cuba Center as native, is Eastern temperate forest region, which you can sometimes simplify as kind of the Eastern half of the United States. We primarily focused on those species; that encompasses some of the Midwest. There is a concentration of Amsonia diversity in Midwestern states, Gulf Coast states, and Southeastern U.S. A little bit eking into the mid-Atlantic, arguably a little bit into Southern Delaware, which we focused on those plants primarily.
There is also another kind of hotspot of Amsonia diversity in the desert Southwest that goes into Northern Mexico as well.
And there are two non-native Amsonia species, and by non-native I mean non-native to North America. One of them is Amsonia orientalis, which is actually native to parts of Europe, in Turkey and Greece. And then there is Amsonia elliptica, which is native to Japan.
And we actually did include for the first time ever in our evaluations an example of a non-native plant, non-native to North America. We included Amsonia orientalis in our evaluation, because of some anecdotal similarities that we have seen between that plant and a plant that’s commonly sold in the trade today, sometimes listed as a native species, as Amsonia ‘Blue Ice.’
Margaret: Yes.
Sam: Yeah. So that was a very interesting thing that we saw after growing those two plants side by side; they’re virtually identical.
Margaret: It looks like ‘Blue Ice’ is in fact derived from parentage that is not a native U.S. plant, yeah?
Sam: Yes. We consider it to be a horticulturally superior form of Amsonia orientalis. So a not-native plant; still a nice garden plant. Pretty much all the Amsonia are good garden plants, but it’s not one that we would want to be promoting because our focus is on Eastern North America and North American native plants. But still available, but again, not one that we are going to be promoting at the end of our evaluation.
Margaret: Right, right. But it’s good that you looked because you had noted this possibility, in that you were able to really over that decade really see it in action and know what were the similarities and deduce a lot more.
Sam: Yeah, absolutely. Yeah.
And I think I read recently on the Lady Bird Johnson Wildflower Center website that even though technically its range maybe extend to somewhere in Virginia-ish up the Southeastern United States, it’s seen in some colonies, naturalized colonies, as far north as Massachusetts. So I wonder if with climate change we’re going to see tabernaemontana become a “wildflower” even up into New England. Do you know what I mean?
Sam: Yeah, very possibly. I mean, even in Mt. Cuba Center we were potentially a little bit outside of its … even tabernaemontana‘s range, which has the largest range of any of the species we’re going to be talking about, or we did talk about in this evaluation. It’s still proved to be a great garden plant. Growing up in New England, Amsonia were planted widely. They’re just extremely adaptable, extremely hardy plants, well outside of even their natural ranges.
Margaret: Yeah. What surprised me was when I saw in the report, and you had done a webinar presentation earlier in February that I had watched as well about when the report was ready with the results and so forth, is that there are different sizes. You see, I think of it as almost … Amsonia, to me, is synonymous almost like sort of a shrubby-feeling structure of a plant.
Sam: Absolutely, yeah.
Margaret: But you had ones in the trial that were quite different, almost groundcover-ish, yes?
Sam: Yes. There were a few plants that would absolutely qualify in the groundcover category. ‘Blue Ice’ is actually one of those plants that is rhizomatous, which was one of the first clues that we’re looking at something different here. This isn’t very similar to Amsonia tabernaemontana. It tends to be very clump-forming, and just continually emerge from that same kind of woody crown that they develop year after year. Amsonia ‘Blue Ice’ has a tendency to spread slowly and eventually does cover ground.
But we had one very unusual plant in this trial. It’s a variety of Amsonia ciliata called tenuifolia and a cultivar named ‘Georgia Pancake.’ [Laughter.] And this was a plant that was originally collect … I love the name. It is the perfect name.
Sam: Yes, exactly. It’s the best name, very descriptive. It is a nearly prostrate-growing plant. It does spread slowly by rhizomes. It was originally collected in Georgia, so it’s ‘Georgia Pancake,’ and it does create this incredible groundcover of this very fine, feathery foliage.
It’s so interesting and so unique, and that’s maybe on the extreme end of things as far as size and stature. Other Amsonia ciliata tenuifolia are just these perfect … They almost look like miniaturized Amsonia hubrichtii. They have that same very fine foliage, beautiful early blue flowers, but they don’t get much bigger than a couple of feet tall and wide. So if you don’t have a lot of space, or even if you have a small rock garden or even a single container, you could grow this plant in your home garden. There’s great options, even if you’re just looking at this overall size of this plant. And again, this is after 10 years of looking at these plants, there are great options for almost any landscape.
Margaret: You just mentioned hubrichtii. And so I think that’s the one that, in more recent years, has come on as a hot plant, so to speak. And I don’t remember exactly where it’s from. I think I have it written down in my notes here somewhere that I looked it up, but I don’t remember. But it definitely has that … The fine texture of the foliage is just so incredibly beautiful.
Sam: It’s wonderful, and it’s such an incredible plant to garden with. The foliage is so fine that it can contrast beautifully just in texture with a number of other plants. It’s a great companion. And jokingly around the office here, we talk about Amsonia flowers a lot, they’re beautiful. The common name, bluestar, refers to the flowers. Of course you want to grow them for that.
But the majority of the year in your home garden you’re going to be looking at the foliage of these plants, which are equally beautiful. They have various textures, really wide-leafed plants, very fine-foliage plants, like thread-like foliage plants like Amsonia hubrichtii. And they just have this incredible movement in the landscape, if there’s a light breeze.
Amsonia hubrichtii [below] can even continue its ornamental season into fall. They can develop really beautiful fall color, especially when you grow them in a lot of sun, kind of ranging from golds to yellows. It can be really, really an attractive season just in and of itself with that fall color.
Sam: Yes, exactly.
Margaret: And it’s like a filler. It serves a role as like a filler, a beautiful textural filler, even when it’s not showing off at one end or the other of the season. So it’s one of those truly, I think (and you say in the report), it’s really a three-season plant. It really does, except when it’s—because these are herbaceous perennials—except when it’s dormant, it really does look great the whole time.
Now they do take some time to get started, is that correct? They’re pretty easy to grow from seed, but they’re slow?
Sam: Yeah, they just take a little time. I think that the biggest challenge with Amsonia is just patience. Just understanding what these plants are going to develop into after a few years in the garden. From seed, it might take three to four years to get your first flowers, but every year that plant’s going to get bigger and it’s going to get more impressive. And it’s going to continue to contribute and pay its rent in the garden space. Every year it’s going to get better.
It just takes a little bit of time. I think of Baptisia in a very similar way. We know there’s going to be a little bit of patients required from us, the gardener, upfront, but we are going to be repaid tenfold into the future as those plants mature and get more established in the landscape.
Margaret: Now, this genus, apparently members of it hybridize with one another pretty freely. It’s a sexy plant [laughter].
Sam: Yes.
Margaret: Yeah. So what’s going on out there and how did you deal with that in a 10-year trial? Do you know what I mean? Were there seedlings being made of-
Sam: Absolutely. Yes.
Margaret: Yeah, so tell us about that, because that’s interesting too.
Sam: Yeah, so in cultivation and even in the wild, Amsonia have proven to be very promiscuous in cultivation. They can cross-pollinate, they can hybridize readily, and you can end up with garden-origin seedlings that have traits that kind of are contributed from two parents. Sometimes the two parents can be obvious, sometimes it’s a little less so.
But sometimes when you’re looking at these hybrids, they can defy categorization. Especially when you’re trying to identify a plant, it can really complicate things. And sometimes in cultivation, if you’re ordering or buying plants and Amsonia from a source where those seeds might be collected in a place where more than one species is present, especially in a cultivated place, you have the potential for hybridization to occur.
In the trial garden, we would just try to stay ahead of seedlings. We would weed things out to try to keep the original collection essentially as it was when we planted it in 2013. That was relatively straightforward to us. But I do think about the potential of some of those plants for a plant breeder or someone who’s introducing interesting new genetics to the horticultural market. A lot of those seedlings, if they were grown out in a field, there could be some really huge potential for the next best thing out there, if you’re looking at it from that perspective.
But yeah, it can be an interesting thing from a plant breeder perspective, there’s a lot of opportunity for new Amsonia or, “improved” Amsonia, if you’re trying to get a more compact plant or you’re breeding in color to the stems or something like that. There’s a lot of potential there. But from a botanical standpoint, it can be confusing [laughter]. So we did try to talk a little bit about some of those features that are good ID features for trying to tease apart some of these closely related plants, but even those can hybridize and can cause it to become a little bit muddied in terms of what you’re looking at. [Below, A. hubrichtii.]
What about aftercare? It’s fall or early winter or late winter if you leave everything standing, what was the protocol that you tried on them? And what do you recommend, having worked with them for 10 years: cutbacks, don’t cut back, whatever. I know they have these hollow stems. Can we take advantage of that? What’s the story?
Sam: Absolutely. Essentially the only time of year that we did anything to these plants was late winter, early spring. Generally we would try to shoot for some time in March. We would cut these plants back, but we always tried to leave a little bit of stem to it. I know Rebecca McMackin has kind of coined the term “garden stubble,” which I really love that, where you leave a little bit of those stems up, 12 to 18 inches, which can serve as habitat, especially for cavity-nesting bees. Because the Amsonia stems have this kind of spongy pith-filled core, bees can hollow into that and nest into it into the next growing season.
And so we tried to do that and we actually did see a lot of those stems being colonized in the later years of the trial, which was very exciting. And it’s just another way for Amsonia to contribute to the overall ecological value of your garden. It’s a great way to double-dip with those plants, as far as providing habitat, and again, ecological value. But that’s all you have to do to these plants, cut them back once a year and just enjoy them for the rest.
Margaret: And maybe not cut them all back all the way to the ground, so you’re leaving some of these, so to speak, open, partially clipped but hollow stems-
Sam: Exactly.
Margaret: … for subsequent use in the years to come.
Sam: Exactly.
Margaret: Yeah. I did some homework, and also in the report you mentioned it, there’s really not a lot of information—and I’m sure it’s out there here and there, but it’s not consolidated, like there is about certain species of plants—about wildlife, other wildlife interactions. You just were describing one where stem-nesting bees could utilize them.
But there’s not a lot of like, “Oh, it’s the host plant for these 47 things and its pollen is utilized by this many …” It seems like it’s not as well-known. And maybe that’s just because … I don’t know why. But you guys observe for interactions as well with pollinators and other creatures, you do some of those observations as well in your trials?
Sam: Yes, especially some of our newer trials, we’re looking at them from those two perspectives, both the beauty and value, which ties back to Mt. Cuba’s mission. We want to inspire people by both. So ornamental quality is being the beauty, giving those plants ratings on their foliage, flowers, all those things. But then the value side of the coin there is most of the time we’re looking at wildlife interaction, and most of the time we’re looking at pollinator interaction between the various species and cultivars were growing in the trial garden.
At the time when the Amsonia were planted at 2013, most of the focus was put onto the beauty side of the plants. But at the end of the trial we wanted to look at pollinator interaction, try to understand if there was any underlying trends, if there were species that were really visiting these plants more so than others. So we did do some pollinator observations in the spring, during the bloom period of 2023.
And over all we saw relatively low numbers of insects on all of the Amsonia. Some of them performed well or performed better than others. But interestingly, the two lowest-performing plants, so the plants that attracted the least number of insects, were ‘Blue Ice’ and Amsonia orientalis. We saw a single insect on both of those plants on only one day out of the multiple weeks of observations that we conducted on all of the Amsonia.
Margaret: And those are the non-U.S. ones?
Sam: Exactly. These are the non-native plants, not offering a lot of pollinator value, at least for what we observed in the trial garden. But we did see an interesting diversity of insects. We saw bumblebees, a host of other native bees, long-tongued flies. We saw a snowberry clearwing moth, which I always refer to as a hummingbird moth. I actually saw-
Margaret: They’re hilarious [laughter]. Yeah.
Sam: They’re lovely. They’re some of the most charismatic pollinators out there. I always get excited when I see them. We even saw monarchs visiting some of these bluestars in bloom.
But one of the really cool things we did observe in this trial was not a pollinator interaction, we actually saw the caterpillars of the snowberry clearwing feeding on Amsonia plants themselves. Amsonia are host plants for a few species of butterflies and moths, but it was really fabulous to see these plants, in cultivation, outside of their locally native range, supporting wildlife as a host plant. That’s very cool. And then seeing the adult moth later in that season, feeding on those flowers, it was very, very cool.
Margaret: If you build it, they will come. Yeah.
Sam: Exactly.
Margaret: Yeah. No. Now, was your trial in full sun? Was it in sun and shade? Were there any other factors that might have affected who visited? Because a lot of times where certain insects choose to feed is also affected by the location, the conditions.
Sam: Absolutely, yes. Location can be a major factor in this. The Amsonia trial was borderline full sun. It was probably right on the edge of what we would define as full sun, six or more hours of sun a day. And because of that, we may have seen less insects, but we also saw not the best display of fall color. On other parts of the garden where the Amsonia were situated in full sun, just anecdotally, we saw a lot more pollinator activity and we also saw better fall color. So probably the best bang for your buck when you are gardening with Amsonia: They can take a little shade, but more sun is better. Probably not just for the ornamental features of that plant, but also for pollinators.
Another thing we were kind of curious about is, were we missing something in this pollinator-watch study? Because we were doing all our observations in the day, was there something happening at night that we weren’t seeing? That was-
Margaret: Like with Phlox paniculata, for instance, where a lot of-
Sam: Exactly.
Margaret: Yeah, you’ll see a lot of nighttime pollinators. Yeah. Huh.
Sam: So that’s a possibility. I think another possibility is that during that time of year, that core season of the Amsonia bloom in mid-May, there are a lot of choices for pollinators around Mt. Cuba Center. I think in some cases, when you have such an abundance of choices, there might be some that are more valuable to pollinators than others, especially when you have such a saturated situation like you do in the naturalistic gardens of Mt. Cuba Center, which are right next door to the trial garden.
So I do wonder if the Amsonia were situated in area where they didn’t have that richness of choices, would we have seen more activity? But still saw some interactions, especially that host interaction was really, really exciting, and something we wrote about in the research report as well.
Margaret: I just wanted to ask, I don’t know if they’re used on the grounds outside the trial gardens or if you’ve ever seen them in the wild growing with anything. Do you have any inspirations on what you imagine them looking good with or what they grow with naturally? Any ideas? Because I’m wanting to add some more, and I’m just curious.
Sam: Yeah, I mean, it kind of depends on the plant, but just at home, I try to add an Amsonia in almost any new garden planting that I have. They’re such a great complement. I think that the flowers themselves … Blue is an unusual color to see in a garden, especially that light sky blue, and it goes with just about anything. I love having it with spring Phlox, for example, that purple goes so well with that blue. Things like wood poppy, that yellow as well. It’s just such a lovely spectrum of colors. Having the Amsonia, especially that later-season foliage and fall color can look really amazing with native grasses.
And then some of these plants that are really small and compact, growing them in a rock garden or growing them in a container with other really small detailed plants can be really, really fun. Speaking with some of the gardeners, playing with texture, having plants with similar texture that bloom at different times and do different things, like planting Amsonia ciliata tenuifolia [below] with things like Liatris microcephala, two similar in appearance plants as far as foliage texture is concerned, but they do very different things. And it’s just kind of a really cool play on how that plant looks, just in foliage.
Sam: Exactly.
Margaret: Same but different. Yeah, cool. Well, Sam, I’m always looking forward to your next … What’s next? I’m ready. I know, I’m teasing, because you get a break.
Sam: [Laughter.] Sure, sure.
Margaret: [Laughter.] What’s next? What are you studying now?
Sam: Yeah, we are doing a lot in the trial garden right now. We have a current evaluation on oakleaf hydrangeas. We’ve just started an evaluation on ferns and on milkweeds, on tiarella. A small trial on Physostegia, and we just planted a trial on Pycnanthemum, or the mountain mints, which I am so excited about.
Margaret: Oh, that’s wonderful. They’re great plants, yeah.
Sam: They’re wonderful plants. They’re great garden plants and pollinators love them. And just the diversity of insects we see just anecdotally at home and in the naturalistic gardens here, I can’t wait to see and really document that in the trial garden going forward. It’s going to be a lot of fun.
Margaret: Well, thank you for making time today, and I hope I’ll talk to you again soon. It’s been great, Sam, as always.
Sam: Absolutely. Thank you so much for having me, Margaret.
(All photos from Mt. Cuba Center, used with permission.)
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