Updated: 3/1/2016
From Nursery to Nature: Are native cultivars as valuable to pollinators as native species?
by Annie S. White
The availability of native plant cultivars is widespread and growing in the nursery & landscape industry. Native cultivars are typically marketed for their ecological benefits, but until now, scientific studies neither supported nor refuted these claims. So are native cultivars as valuable in pollinator habitat gardens as the true native species? The answer is complicated; some cultivars are and some cultivars aren’t.
Initiatives to address pollinator decline are widespread and growing in the United States. Pollinator-friendly landscaping and land management practices aim to preserve or restore floral-rich habitat in urban backyards, in agricultural landscapes, and everywhere in between. Enhancing floral resources can improve the abundance and productivity of domestic honey bees, wild bees, and other insect pollinators, even in landscapes with little natural habitat.
Several studies suggest that wild bees prefer to forage—but not necessarily exclusively—on the nectar and pollen from native plants. Native plants are also typically well-adapted to local soil, climate, and other environmental conditions, making them more durable in the landscape. For these reasons, native plants are frequently recommended for pollinator habitat restoration and pollinator garden projects.
The growing demand for native plants in ecological landscaping, including pollinator habitat gardens, has led to the selection and breeding of native cultivars. A native cultivar or “nativar” is a cultivated variety of a native plant, that has been selected by humans (in nature or through repeated selections in a breeding program), cross-bred, and/or hybridized by botanists and plants breeders seeking desirable characteristics that can be maintained through propagation.
The flowers of native cultivars may vary from the native species in size, shape, abundance, color, and bloom time—all attributes known to influence pollinator visitation. In addition to floral traits, native cultivars are sometimes selected for disease resistance, and more predictable sizes and shapes than their wild relatives, making them more desirable landscape plants. But native cultivars can also be less hardy and may prefer different soil moisture and fertility than the species, and most serious of all, may not be as attractive and useful to pollinators.
Some of the traits that humans find attractive in native cultivars, such as a double flowers or an unusual color, may make the flower less attractive to pollinators, and furthermore, may decrease the quantity, quality, and accessibility of the nectar and pollen rewards.
The use of strongly selected cultivars is generally discouraged in ecological restoration projects, but native cultivars are widely available and widely used in the landscape industry. In fact, when gardeners visit their local garden centers, it’s often impossible to find true native species. Gardeners can find echinaceas in every color, size, and shape possible, but will struggle to find a non-cultivated variety of Echinacea purpurea or Echinacea pallida.
With the National Pollinator Garden Network aiming to register one million pollinator gardens; the Pollinator Health Task Force aiming to enhance seven million acres of land for pollinators; and bee habitat on private farms remaining a priority of all conservation programs under the U.S. Farm Bill, it’s important that we understand if native cultivars are comparable substitutions for native species, and if they can perform the same ecological functions in pollinator habitat gardens.
Since 2011, I have been studying this topic at multiple field sites in northern Vermont (zones 4a and 4b) as a PhD student in Plant & Soil Science at the University of Vermont. Under the guidance of Dr. Leonard Perry, I established replicated experimental pollinator gardens to monitor pollinator visitation to 12 native species and 14 native cultivars, to evaluate their garden performance, and to study patterns of nectar production in an additional two native species and four native cultivars.
Some native cultivars attract just as many insect pollinators as the native species. This was seen mostly for open-pollinated seed cultivars such as Asclepias tuberosa ‘Hello Yellow’ and Monarda fistulosa ‘Claire Grace.’ (However, it’s noteworthy that ‘Claire Grace was not as cold hardy in zone 4 given that it’s a selection from a southern ecotype.) One native cultivar selection, Veronicastrum virginicum ‘Lavendelturm’ actually attracted significantly more total pollinators than the native species and had a longer bloom time. This illustrates that there’s potential for pollinator-friendly cultivars (with long bloom periods and high nectar production) to be selected for and marketed.
One clear trend was observed across all species; the more manipulated the cultivars became, the less attractive they became to pollinators. Cultivars such as Achillea millefolium ‘Strawberry Seduction’ and Symphyotrichum novae-angliae ‘Alma Poetschke’, which are the result of repeated selections in breeding programs, attracted significantly fewer pollinators in nearly all pollinator groups. The same held true for hybrid varieties from breeding programs such as Baptisia x varicolor ‘Twilite Prairieblues’ and Tradescantia ‘Red Grape,’ Echinacea ‘Sunrise’ Big Sky and Echinacea ‘Pink Double Delight.’
Although our research doesn’t answer why some pollinators strongly preferred the native species, we hypothesize that color differences and decreased nectar and pollen production in hybridized cultivars are the leading factors.
We also studied patterns of nectar production (in other words, the quality, quantity and distribution of the floral reward) in Lobelia cardinalis (hummingbird pollinated), L. cardinalis ‘Fried Green Tomatoes,’ L. cardinalis ‘Black Truffle,’ L. x speciosa ‘Fan Scarlet,’ L. x speciosa ‘Fan Blue,’ and L. siphilicata (bumble bee pollinated). This study showed slightly decreased nectar volumes in ‘Fried Green Tomatoes,’ comparable nectar in ‘Black Truffle,’ and significantly decreased nectar volume and nectar sugars in the L. x speciosa hybrids, which are crosses between L. cardinalis and L. siphilitca. L. x speciosa ‘Fan Scarlet’ may perform nicely in the garden and may lure hummingbirds to its bright red tubular flowers, but these pollinators are being rewarded with less than 20% of the nectar energy that they would find in the native species, Lobelia cardinalis.
Results may vary in other regions and with other native species and native cultivars, but this research highlights that in some cases, pollinators (bees, in particular) exhibit strong floral preferences for native species. If evaluating native cultivars for use in a pollinator habitat garden, try to limit the use of cultivars to open-pollinated seed-grown “selections” or “sports” of the native species. Cultivars that differ significantly in color and morphology from the native species should be used cautiously and cultivars with hybrid origins should be avoided in the context of pollinator habitat restoration.
This research is just the beginning of what needs to be many more scientific evaluations of native species and all their cultivars.
Three of our research projects related to native cultivars are currently in preparation for publication in 2016. Stay tuned!
Pollinator Gardens.org 
Nice project. I appreciate your efforts! I think my take-away is, or rather remains, that each species -and its associated cultivars, ie. nativars-must be evaluated on its own merits. It is precisely work like you are doing, that is needed to make these evaluations. Thanks!
Annie, I met you at the Pollinator Conference poster session and you gave me a couple of sheets on your results so far. I am so glad you are continuing this. I am giving 2 talks shortly, one on Creating Pollinator Habitat in Our Living Spaces in which I address cultivars and another on Genetic Diversity vs. Cultivars and Clones. Could I use some of your material posted above?
Bees prefer simpler blooms. A single petaled echinacea bloom will attract more blooms than a double. I do not understand why this was not mentioned in the article.
I am glad this was shared on Facebook where I could see it. We have a small yard in SE Nebraska, and over the years, have taken most of the lawn out. When I first figured out there were native plants that could be grown in a flower bed, the ones that were available were frequently cultivars. Some came with tags that said they were native plants. It was confusing to me until I learned to read the tag. Still, there were times when the tag saying it was native had writing on it, saying the name of the cultivar it actually was. I do have lots of pollinators, and since I am in the city, and not on an acreage, it’s not as critical. I am seeing more native plants being offered, but I am hoping to see even more in the next few years.
Thanks for the work you are doing!
The article did address what Trudi mentioned.
A statistical note that I don’t think would change the overall pattern, but which might affect a small number of the comparisons. There are many, many comparisons being made, and if you use an alpha of 0.05, the possibility of type I errors for specific contrasts is very real. Many of comparisons have p less than or equal to 0.0001, which would still be significant with an alpha adjustment (dividing 0.05 by the number of contrasts). All of that said, there are a lot of ways to statistically model the data, and I’m aware this post isn’t a journal submission.
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Hi Annie,
I’m working on a white paper to help establish our policy of not using native cultivars in restoration. Do you have a paper published in a peer reviewed journal I could reference? Thank you very much. I have searched using Google Scholar and found nothing. I don’t have academic resources unfortunately.
Susan
We are building be and native pollinator habitat on our organic farm in SE Ohio and very glad glad to see your research. Looking to work with other researchers as we consider expanding into an apiary.
Research such as yours is important as we try to sort out the many vagaries of the term “native.” To wit, according to the most popular range maps on the internet (USDA and BONAP) a number of the species in your posted chart are not known to be native to Vermont. Even when extirpated and adventive species are included (as in the USDA maps, which don’t differentiate as does BONAP), only 2/3 of your “native” species are, or once were, found natively in Vermont. I realize the imperfection of range maps, but I always struggle with how close nativity needs to be to really matter. It would be interesting to me to know which, if any, truly native Vermont species outperform the near- and not-so-near “natives” in your study.
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I just happened to make it to the VBA winter meeting in time to catch your presentation and I must say, it was the most interesting and exciting research I’ve heard about in a long while. Great work and thank you so much for sharing. Somehow I think I’ve managed to share at least some tidbit of what you presented with most of my friends, family and coworkers! Congrats on the PhD!
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“‘Fan Scarlet’ may perform nicely in the garden and may lure hummingbirds to its bright red tubular flowers, but these pollinators are being rewarded with less than 20% of the nectar energy that they would find in the native species, Lobelia cardinalis.”
This caught my eye. What are the chances that cultivar traits which could be considered negative, such as reduced nutritional value, might disperse through native populations? Could this lead to contamination of native genes or is this a non-issue?
I’m no geneticist, so forgive my ignorance.
“Cultivars that differ significantly in color and morphology from the native species should be used cautiously and cultivars with hybrid origins should be avoided in the context of pollinator habitat restoration.”
What are cultivars with hybrid origins? Aren’t all cultivars hybrids? Feeling confused!
Annie have you published this yet? I am downloading your thesis for weekend reading. This has been one of my major wonders over the last 12 years of research.
Maria
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Janette…..some cultivars are naturally occurring ‘sports’ of the parent plant. However, other cultivar hybrids are taking two different native plants within the species and crossing them to get certain qualities.
I was glad to see that the yellow butterfly weed was as good as the naturally occurring orange species. For me it is another colour to offer in my plantings.
reference? I’d love to see the papers!!!
What about dwarf species (eg drawf echinicea purpea or NE aster)? Presumably these have been selected for size and not cross bred, so their performance should be similar to the original species, although with perhaps lower levels of pollen/nectar given their reduced size…?
A couple years ago when I first became interested in this issue, Dr. White’s was the only research I could find. Lots of opinions, but no research. Her dissertation is published. Just search on her name and a subject of horticulture or native plants and you can read the whole thing and debate to your heart’s content about statistical analysis and P values. Several botanic gardens are working on projects of evaluating natives vs. nativars, Denver Botanic Garden in my own state of Colorado among them. so look for more data to be available soon. FYI, cultivars can be hybrids between two (or even more) related species, but also can just be selections. Native plants will “naturally” hybridize. Columbine and Penstemon are two well-known examples that hybridize in the garden, and Castellija sp in the wild, especially now that some species are changing their range due to climate change.
I’m looking forward to the research. Perhaps seed catalogues in the future will be able to properly and accurately list their cultivars as pollinator friendly, or not.
Is there a list or database of cultivars showing which are better or worse for pollinators, perhaps by region?
Very interesting and useful information, I grow a wide range of pollinators plants and monitor those visited by insects .Fully agree that cultivars may not be as pollinators friendly as orginial species.
I watched Dr. White on-line through Claudia Thompson’s Native Plants organization…really terrific…looking forward to a book being published!
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The chart listing preferences for natives vs cultivars is unreadable. Can I get a copy of it?
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Really helpful piece; your explanation of how native cultivars can “sometimes, in some ways” benefit pollinators is the clearest I have read anywhere. Thanks so much for the work you’re doing.
Somehow your comment got sent to me. I think you want to contact Dr. Annie White.