Is a flower by any other name still the same? Not necessarily. Research has found that some native cultivars grown for aesthetic traits have less wildlife value. Here’s what you should know.
When my favorite diminutive summer vacationers start arriving early in the season, I like to ensure they have a five-star experience. The hummingbird menu starts with an array of tasty tubular flowers: bright red bee balm, lavender wild bergamot, columbine, red buckeye, coral honeysuckle, trumpet creeper, cardinal flower, phlox, penstemon, and blazing star. My garden B&B also includes native plants that attract insects the birds need to round out their sugary diet.
Watching these tiny migrants enjoy the diverse buffet is a source of hope for me. It’s inspiring to know that the simple act of planting flowers can ensure the birds won’t go hungry.
Not all supposedly native plants are created equal; some grown to satisfy human-desired characteristics appear to have lost traits helpful to birds, bees, caterpillars and other animals.
But though the offerings seem as popular as a picnic on the beach, recent research shows that some of the ingredients may be about as nutritious as cotton candy. In spite of appearances, an animal’s repeated return to a plant doesn’t necessarily mean he’s getting the nourishment he needs. Not all supposedly native plants are created equal; some grown to satisfy human-desired characteristics appear to have lost traits helpful to birds, bees, caterpillars, and other animals. Called “cultivars,” these manipulated plants are bred or selected for delayed bloom times, larger flowers, varying colors, dwarf stature, and other qualities considered useful or interesting in the garden setting. Some are variants originally found in the wild, while others are bred repeatedly—or, in the case of hybrids, crossed with related species—until the desired effect is achieved. In the process, they may have lost both inherent value to wildlife and sensory cues that attract animals to the plants in the first place.
As a gardener for the past two decades, I don’t always know or remember the exact provenance of plants added years ago. Though I’ve grown some from seed, many came from nurseries and friends. When the hummingbirds visit a cardinal flower, I’m not sure anymore whether it was the cardinal flower my mother-in-law gave me, the cardinal flower I bought at a native nursery, or the cardinal flower a friend divided and shared from her garden—let alone whether they are cultivars or strictly native species that evolved with the animals who depend on them.
Why does this matter? For more answers, I talked with Annie White, a Vermont ecological landscape designer who devoted her doctoral research, published online last week, to comparing how frequently pollinators visit native species versus their cultivars. She is also preparing a paper that quantifies nectar production in cardinal flower species and cultivars. Two primary questions underlie these efforts: Do changes in shape, color, growth habit, or bloom time reduce attractiveness to bees, butterflies, and other pollinators? Do such changes also affect the ability of the flower to deliver the floral resources offered by unmanipulated plants? Though results are mixed and no single answer has emerged, her work provides a better picture of how human aesthetic preferences may spell trouble for our wild friends.
Q: A lot of times people see pollinators visiting a plant en masse and assume that the flowers are great for those animals. But from what I gathered from your research on cardinal flower hybrids, a bloom may be very attractive to an animal but not necessarily provide the needed nutrition.
What’s really fascinating is that Lobelia cardinalis is hummingbird-pollinated and Lobelia siphilitica is bumblebee-pollinated. The morphology of the flowers has evolved specific to their pollinators, with the cardinalis having a really long and narrow corolla tube which a bumblebee can’t get inside. Also, the red color of the flowers is more attractive to hummingbirds and not so attractive to bees.
I was looking at the quantity and the quality of nectar production within these species and these hybrids. So I found that the native species Lobelia cardinalis has really high nectar production, which makes sense because it needs to be providing energy for hummingbirds, and hummingbirds require more energy than a bumblebee would. Whereas Lobelia siphilitica, being bumblebee-pollinated, has a much lower quantity of nectar in the flowers—which is much more in line with what a bumblebee would be needing per visit.
But now there are these hybrids that are really popular in the garden industry—usually Lobelia x speciosa. So that just made me really curious: Well, what about these hybrids? Who’s pollinating those? And both of the hybrids I looked at had highly diminished nectar quantity, even a little bit less than Lobelia silphitica. It’s really concerning with the Lobelia x speciosa cultivar ‘Fan Scarlet’ because the color is red, and it has a more similar morphology to Lobelia cardinalis. And so it attracts hummingbirds, but then the hummingbird is only getting about 20 percent of the energy from that flower that it would get from the native species itself. It’s luring the hummingbird in but not giving it the reward that it’s expecting to find.
Q: If the flowers aren’t providing what hummingbirds would normally get, that means that they keep coming back but are expending too much energy?
Yes, I think that would be the hypothesis—that they’re expending a lot more energy to find these flowers. And also if you have a small garden space and you’re trying to fill it with flowers that are going to be the most beneficial, you’re going to be able to pack a lot more benefits for the hummingbirds and other pollinators by using the plant that has the optimal nectar production and not just something that’s taking up your garden space but isn’t providing the same benefit.
Q: Your other research focused on comparing the frequency of pollinator visits on native species versus their cultivars. Have you had any reaction yet from others in the nursery industry in terms of helping people make educated choices? Many people aren’t going to know about this because even at native plant sales there are still lots of cultivars.
It’s really tough because what I’ve found is that about half of the cultivars that I looked at were comparable to the native species, and about half were inferior. I did find one that was actually better. That was a Culver’s root, Veronicastrum virginicum ‘Lavender Towers.’ So it does seem like there’s a lot of variation—that not all cultivars are going to be the same or less beneficial. We just need so much more research. That’s a real weakness right now, and I think what I’ve shown is—particularly as we’re putting more and more cultivars out on the market—we need to really make plant breeders aware that they are sometimes putting out these cultivars that are inferior in terms of their benefits to pollinators. I’ve had a tremendous amount of interest from growers and even from some breeders and certainly from gardeners who want to know more about this. And it’s something that they’re just learning about for the first time.
The New England asters that I studied showed one of the largest differences that I saw between the native and the cultivar ‘Alma Potschke’—like 20 times more pollinators on the natives than on the cultivars. That was one that really surprised me because the flowers are very similar morphology, the same size, and they were blooming at exactly the same time. They just had a color difference.
Q: What do you tell gardeners who ask for recommendations?
In general my suggestion to people is to use the native species as much as possible. If you are considering using cultivars for whatever reason, whether it’s disease resistance or shorter stature, choosing a cultivar that’s as close to the native species as possible—in its morphology and in its bloom time and in its color—is going to increase the likelihood that it’s a comparable substitution. And try to certainly avoid things like double flowers—it’s been well-documented that double flowers have decreased nectar and pollen availability and accessibility. Be really leery of hybrids.
Q: Have you seen problems in hybrids beyond the lobelias?
I’ve seen that in the echinaceas for sure. I’ve observed several echinacea hybrids, and all of them have been inferior. I did have one in my study that’s well-documented.
Q: When you first started thinking about this, was there already talk about it, or was it something that you anecdotally observed in the field?
It was something that I had just observed. At the time I was an ecological landscape designer. I was in the Midwest in Indiana working for a company, and we had a native plant nursery and also we had large seed production beds. So one of my favorite things was just to go out at lunchtime and
wander through these seedbeds of various flowering native plants. And that’s how I got interested in pollinators. And the spiderwort
[Tradescantia spp.] amazed me the most when it came into bloom in early summer; it would just be just buzzing with pollinators. And I had seen on smaller sites some of these garden varieties of the tradescantia being planted, and I noticed there were very, very few pollinators if any on them. And another person even mentioned the same thing—that they felt like some of these cultivars, these garden varieties, didn’t seem like they were as attractive to the pollinators. That was kind of one example that really got me thinking about it.
And I had a lot of cases where I was designing native plant gardens—I would then turn that list over to a contractor to have them actually install the project and would go back to check the site to see that they had put in all cultivars or had substituted a number of plants with cultivars. And they felt like that was justifiable because it’s the same genus and species. A lot of times the contractors don’t even know—they assume that a genus and species is as specific as you can get.
Q: When you verified in your studies that the native spiderwort was visited a lot more by the pollinators than the cultivar, you concluded that the discrepancy may have been a result of the differing bloom times—that perhaps bees emerging just in time for the straight species’ blooms are out of sync with later-blooming cultivars. Were there other cultivars that seemed out of sync with seasonal needs of pollinators?
Well, there was one—sneezeweed, or Helenium autumnale. I looked at a cultivar called ‘Moerheim Beauty.’ They had completely different bloom periods. With a lot of the cultivars, it was oftentimes a week or maybe a two-week difference, and the bloom period would typically overlap. But with those two it was a stark difference. The cultivar bloomed in midsummer, and the native blooms really late, in September and even into October. So there was no overlap whatsoever, and there was a huge, very dramatic difference in terms of pollinator attractiveness. But because the native blooms so late, it’s a really important plant because there’s so few other floral resources available during that time.
I had so many confounding variables because there also was a color change, It was a red cultivar versus the native being yellow; it also was just a plant that didn’t perform as well. So it’s hard sometimes to tease out exactly why these things are happening. I know for sure I have documentation that the pollinators were visiting the natives significantly more, but I can only hypothesize still as to why that’s happening.
Q: I talked to an entomologist last year who was aware of the research but complained that straight-species asters fall over and said she doesn’t want that in her garden. Is it possible to design around some of these attributes to get people more interested in these plants?
Truthfully, I do a lot of gardening myself, and I still use some cultivars—and even cultivars that I know are a little bit less beneficial to pollinators, just because in some circumstances, you know you need an aster for a border that’s not going to be 4 feet tall and flopping over. Or you need a joe-pye weed that’s not 8 feet tall; you want something that’s more like 4 feet tall. You know something won’t work in this specific scenario that you need it to work in unless you do choose a cultivar.
So I’m not completely against cultivars. I think there are still certain settings where they make sense. There’s also been some benefits in terms of disease resistance, where they’re trying to find monardas that are more mildew-resistant. So there can be some benefits there, but I think the risk is that you’re also creating these plants that may not be as beneficial.
Almost across the board, I found that all of these cultivars that are selected for shorter stature or more compactness just don’t have as many flowers, so they’re not producing as much nectar and pollen.
Almost across the board, I found that all of these cultivars that are selected for shorter stature or more compactness just don’t have as many flowers, so they’re not producing as much nectar and pollen. Also for me being up in Vermont—I’m in zone 4a and 4b—a lot of these cultivars had real problems with hardiness compared to the natives. So where you are in Maryland, that may not be as big of an issue. But I had a Monarda fistulosa ‘Claire Grace’ and learned as I researched how these plants were developed that it was actually a selection from down in Mississippi, I believe. So it makes sense that that selection, that species coming from far down south is not going be hardy in northern Vermont. But they sell it in the garden centers; I see it all the time. That’s not really information that ends up getting passed on to the garden centers or certainly to the consumer.
Q: You did a lot of bee watching during your research. Did you learn other things that weren’t part of this study?
Yes, I think one of the really remarkable things that I noticed—and that I do have a lot of data on, even though it’s not really the focus of the paper—was just how different pollinators have very different floral preferences. And I think that’s really a weakness of all of these pollinator planting lists that are out there in circulation; they’re really not specific for their pollinator types. And there are really big differences between what butterflies are foraging on versus what bees are, and really big differences between honeybees and bumblebees. So when doing a pollinator garden, you almost have to decide, well, what pollinator species am I trying to help the most? If you’re a honeybee keeper and you’re looking for a forage garden for your honeybees, there are a number of things that you could plant that are really common on pollinator planting lists but that actually have no benefits for your honeybees. Baptisias are only really pollinated by bumblebees because they’re the only pollinator that’s strong enough to get inside the flower. Or rudbeckias—I almost only saw a lot of the really small native bees on there.
I think there’s been quite a bit of research on the phlox cultivars. At the Mt. Cuba Center, they had a cultivar that did really well, and I keep seeing people promoting that one cultivar as this amazing pollinator plant. But phlox is a butterfly-pollinated plant for the most part. It’s really difficult for bees to access the nectar and pollen, so it’s very specific to butterflies.
Q: So if you’re trying to help bees, that plant won’t do it. What else can gardeners do to become more aware and select more wildlife-friendly plants?
For people who do have strictly native plant nurseries in their regions, one easy thing is to try to shop there first because you’re going to know that a well-respected native plant nursery is going to be growing native species, that they’re going be trying to maintain genetic diversity within that population. That’s a whole other aspect of cultivars that’s a little bit troubling—the loss of genetic diversity.
Q: Because if they’re reproduced for sale clonally—which most of them are—they’re all essentially the same plant, right? And then the plant populations can lose resiliency.
Right, exactly. I like to use the cardinal flower as an example again: If I live adjacent to a natural area that’s full of native cardinal flower and I put a cultivar in my garden, or if, let’s say, I want a garden full of red and I put a hundred of those in my garden, those are going to cross-pollinate with the natives.
Are we going to end up genetically polluting our natural areas with the genetics of these cultivars that aren’t as strong, that don’t have natural resiliency built into them?
And if all of these cultivars are just clones of each other and maybe they’re from a genetic stock from down south, and maybe that selection just happens to be less disease-resistant, are we going to end up genetically polluting our natural areas with the genetics of these cultivars that aren’t as strong, that don’t have natural resiliency built into them?
I’m not aware of anyone doing research on that, but I think it’s really, really important.
For More Information
Read the full study: Annie White’s thesis, “From Nursery to Nature: Evaluating Native Herbaceous Flowering Plants Versus Native Cultivars for Pollinator Habitat Restoration,” was published July 19 and is available for download. For a quick summary of her research, see her website, PollinatorGardens.org. You can also catch up with White on Facebook and Instagram at @nectarlandscapes.
Other cultivar research: The Mt. Cuba Center has been conducting extensive research on the value of cultivars; though much of this is focused on growth habit and performance in the garden, a citizen science project quantified pollinator visitation to monarda cultivars, and a collaboration with University of Delaware scientists catalogued bee preferences for coreopsis species and their cultivars. UD and Mt. Cuba have also partnered to examine the value of cultivars of woody plants for caterpillars. While some have shown equal benefits, others are poor substitutes; cultivars bred to have red leaves, for example, are loaded with anthocyanins (pigments that deter feeding) and don’t attract as many caterpillars as the greener straight species.
Definition of terms: Cultivar? Variety? Hybrid? What does it all mean? Among the many good explanations are these from Virginia Cooperative Extension and Nebraska Cooperative Extension. An important note to remember while shopping: When looking at a label, single quotes around wording that follows the species name indicates the plant is a cultivar; e.g., Lobelia cardinalis ‘Fan Scarlet’ or Monarda fistulosa ‘Claire Grace.’
Gardening for bees: For more information about nurturing wild bees through planting and gentle cultivation, see “How to Really Save the Bees.”
(Featured images of Echinacea purpurea with swallowtails and Lobelia cardinalis with hummingbird by Nancy Lawson)