In this post, I cover the 2009 paper, “Impact of native plants on bird and butterfly biodiversity in suburban landscapes,” by Karin Burghardt, et al.[i]
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This study was published shortly after the first edition of Doug Tallamy’s book, Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens.[ii] After decades of studying host plant records of butterfly and moth species, Tallamy was convinced that native plants were critically important to wildlife conservation. About half of all insects are herbivores, and about 70 percent of all herbivores are specialists that are only capable of feeding on a narrow range of plants (see Schoonhoven et al. 2005, Chapter 2, pages 5-9). Specialist insects have developed, over time, the ability to feed on plants that have physical or chemical deterrents that keep generalist insects at bay. Although specialist insects can feed on plants that can be toxic to other insects, they can’t easily switch to feed on novel, non-native plants.
Burghardt and Tallamy’s Study of Native Plants and Caterpillars
Tallamy was Karin Burghardt’s master’s degree advisor and one of her co-authors on the 2009 paper. In their study, they selected six pairs of suburban gardens in central Pennsylvania. Gardens were paired by size and proximity. One garden in each pair featured the conventional landscaping for this region: large lawns, Asian shrubs, Asian understory trees, and native canopy trees. The other garden was landscaped with native ornamentals at each vegetative layer: grasses, shrubs, understory trees, and canopy trees.
They counted the number of caterpillars at 12 points within each garden. Since caterpillars are herbivores, and most insect herbivores are specialists that do best on native plants, they hypothesized that they would find more caterpillars in the native plant gardens. Indeed, this is what they found. Caterpillar abundance was four times greater, and caterpillar species diversity was three times greater, in the native gardens versus the conventional gardens. In addition, Burghardt found that native plant gardens harbored more birds. In fact, native plant gardens had 55 percent more birds and 73 percent more bird species, compared to conventional gardens!
This study demonstrated that gardeners’ choices matter and can clearly influence ecological food chains. Food chains are organized into what are known as trophic levels. Organisms on the same trophic level share the same ecological function and nutritional distance from the sun. Photosynthetic plants are on the first trophic level. Herbivores, or organisms that eat plants, are on the second trophic level. Organisms that eat herbivores, such as birds, are on the third trophic level.
Burghardt and Tallamy demonstrated that what you decide to plant in your garden not only determines the structure of the first trophic level but can also cascade up to affect the second and third trophic levels. As an entomologist, I was not surprised that gardeners’ plant selections could influence the second trophic level. However, I was blown away that these decisions could cascade up to strongly influence the third trophic level.
Garden Ecology Lab Studies of Native Plants and Bees
In the Oregon State University Garden Ecology Lab, we study relationships between native garden plants and native bees. To be honest, I did not expect that native bees would prefer native plants. Whereas the leaves and other vegetative parts of a plant include an array of chemical and physical defenses to protect the plant from insect herbivores, flowers have few such defenses. In fact, flowers function to attract pollinators to a plant.
Thus I was somewhat surprised when Ph.D. student, Aaron Anderson, found that most of the native plants in his study attracted more native bees and more species of native bees than his non-native comparison plants. For example, non-native lavender ‘Grosso’ attracted a large number of bees, but most of these bees were non-native honey bees. By and large, the native plants were better for bee abundance and bee diversity, compared to the non-native comparison plants. In particular, Globe Gilia, Farewell to Spring, Oregon Sunshine, Douglas Aster, and California Poppy were all particularly attractive to native, wild bees in Aaron’s study.
Why might native bees prefer native plants, when flowers don’t have the same chemical and physical deterrents that herbivores must contend with? One hypothesis is that the nectar and pollen in native plants might provide better nutrition to native bees. Another hypothesis is that pollinators are keenly tied into the visual display of native plants. Flower color, size, shape, and ultraviolet markings are all important signals that flowers use to attract the attention of various pollinators. If there are changes in any aspect of this visual display, pollinators may no longer recognize a flowering plant as a good source of pollen or nectar.
Another OSU Ph.D. student, Jen Hayes, is trying to understand why native plants seem to be preferred by native pollinators. As part of her Ph.D. work in the Garden Ecology Lab, Jen is collaborating with an OSU photography student, Svea Bruslind. Svea uses different filters to take photographs of native plants and native cultivars in visible light, ultraviolet light, and in “bee vision” light. We are just getting started on this study, but look forward to reporting our findings in the near future.
[i]Burghardt et al. 2009. Impact of native plants on bird and butterfly biodiversity in suburban landscapes. Conservation Biology 23:219–224.
[ii] Updated and expanded version published as Bringing Nature Home: How You Can Sustain Wildlife with Natives Plants.
According to the staff at Oak Creek and many other gardeners and farmers I’ve had the opportunity to talk to, it appears that though 2020 was a difficult year for humans, it was truly a remarkable year for gophers and other rodents.
From left to right: wild type Great Camas, Camassia leichtlinii, the native cultivar ‘Sacajawea’, and the native cultivar ‘Caerulea Blue Heaven’.
Gophers & Camas
No matter how often a gopher was trapped and removed from Oak Creek last summer, the next week there would always be a mound of freshly turned soil on the grounds, indicating a new gopher had taken its place. While they seemed to enjoy popping up in some of the Organic Gardening Club’s beds, they had an extra fondness for my own experimental garden beds. Fresh gopher-turned soil was most commonly found in any plot growing our native Camassia leichtlinii (Great Camas) and the plots surrounding them.
Bulb size comparisons for the three varieties included in our study.
We planted our 15 camas plots in the fall of 2019. Five plots were planted with the wild type camas species, Camassia leichtlinii (Great Camas). Five more were planted with the C. leichtlinii cultivar ‘Caerulea Blue Heaven’, and the final five were planted with C. leichtlinii ‘Sacajawea’. By the spring of 2020, the camas plots were relatively untouched, aside from some minor grazing by deer on a handful of plots. In April our three camas varieties began blooming in sequence (the native first, followed by ‘Blue Heaven’ and ‘Sacajawea’, respectively), and by mid June they had all gone to seed.
Deer browsing on early spring shoots of C. leichtlinii ‘Sacajawea’.
Though the gopher troubles seemed to really begin in June, there were signs of their activity that we did not heed. In spring of 2020 I was planting a Clarkia amoena cultivar plug. Upon removing some soil to make room for the plant, I found that the soil seemed to drop off into a massive hole beneath the plot I was planting. I shook some soil loose to fill the hole, planted my Clarkia, and moved on. Later in the season, a different Clarkia plant would be found dead, and upon its removal, another tunnel would be found beneath the top layer of soil.
By August, there had been so much gopher activity in our beds that I decided we needed to conduct a damage assessment. I asked Tyler to dig around in a Camas plot that seemed particularly ravaged by the gophers, to see if he could find any of the original 40 bulbs we had planted. His searching returned no bulbs.
Bulb Thieves
I immediately went through each of the 15 camas plots and rated them with a visual assessment of the gopher activity that we would use to determine how many bulbs likely remained in the plots. The levels we decided on were “low/no damage” “Low damage”, “Moderate Damage”, “High Damage” and “Extreme Damage”. Plots with no damage were expected to have all 40 original planted bulbs. On the other end of the spectrum, plots labeled “Extreme” were expected to have no remaining bulbs.
At the end of our field season, we dug out the bulbs from each of the camas plots so we could assess the actual damage, and so we could install fencing to keep all future gophers out. During the bulb dig, we recorded the total number of bulbs found in each plot. In the table below, I have shared the visual damage rating for each plot, the estimated number of bulbs expected to be in the plots, and the actual number of bulbs we found.
Rep #
Bulb Type
Visual Damage Rating
Estimated Remaining Bulbs
Actual Remaining Bulbs
1
Blue Heaven
Low-no
40
2
2
Blue Heaven
Low-no
40
66
3
Blue Heaven
High
10
53
4
Blue Heaven
High
10
66
5
Blue Heaven
High
10
5
Totals
110
192
1
Native
Extreme
0
0
2
Native
Low
40
8
3
Native
Extreme
0
8
4
Native
Extreme
0
30
5
Native
High
10
3
Totals
50
49
1
Sacajawea
High
10
0
2
Sacajawea
High
10
0
3
Sacajawea
Moderate
20
0
4
Sacajawea
Low-no
40
0
5
Sacajawea
Moderate
20
0
Totals
100
0
Table 1: Camas Plot Estimated and Observed Damage. Damage values are estimates of how many of the original 40 bulbs are likely to remain in each plot.
While our findings from this unexpected study of bulbs were unfortunate, they tell an interesting story. An important point to note is that many of the bulbs have divided since they were planted, which is why in a few cases we found more than the original 40 planted bulbs. Regardless, there is a clear preference for the native C. leichtlinii and native cultivar ‘Sacajawea’ bulbs over the ‘Blue Heaven’ cultivar. We also noticed that any bulbs that were planted more shallow than the recommended 2-3x the height of the bulb were missed by the gophers.
Finding the Gopher Stash
After the exploratory bulb digging, we excavated each of our camas plots to around 1 foot in depth to install fences to keep the gophers from returning to our plots. While digging out the excess soil, we would often find a bulb or two that weren’t located during the initial bulb removal (these numbers are not included in Table 1, as we did not record them). In one section where the three camas types were planted in a row, we excavated a huge section of the garden, and made an amazing discovery (extra Kudos to Tyler who did the bulk of the work on this section).
On one of the walls of the hole, we found a gopher food chamber with thick white roots sticking out of the bottom of it. We removed some soil from the entrance, and discovered a chamber filled with camas bulbs. We carefully removed them and found over 60 bulbs that had been stolen from our plots.
The 3excavated plots, the food chamber, and the pile of 66 bulbs removed from the burrow.
Some of the bulbs were clearly the wild type great camas, identified by their characteristic long neck. The others we suspect to be ‘Sacajawea’ bulbs, as the burrow was found in what used to be a ‘Sacajawea’ plot. Any unknown bulbs were brought to my home and planted in a planter box to be identified in the next couple of months. The ‘Sacajawea’ bulbs have variegated foliage, making them easy to pick out once their shoots appear above the soil. We won’t know if the remaining mystery bulbs are ‘Blue Heaven’ or large wild type bulbs until they bloom in the spring.
Moving Forward
On the left: Jen (me) building a gopher exclosure. On the right: Tyler finishing installing a gopher exclosure.
In November of 2020 we installed our fences, refilled the gaping holes with soil, and replanted all of the camas bulbs, including some supplemental purchased bulbs of each of the three varieties. The native Camas and ‘Blue Heaven’ were successfully replanted with 40 bulbs. We were only able to order enough ‘Sacajawea’ bulbs to achieve a density of 30 bulbs per plot, though they will receive additional geophytes if any of the mystery bulbs turn out to be variegated. The mystery bulbs have yet to push their shoots through the soil, but I will include an update on their identities when I have them.
Thank you to Tyler, Izzy, Max, and my fiancé Elliot for helping out in this laborious process. I absolutely would not have been able to safeguard the new camas plantings without your efforts and support in this process.
This past year presented challenge and change to the Garden Ecology Lab. COVID locked us out of the lab and out of the field for a period of time. We said goodbye to two lab members (Angelee graduated! Cliff decided to move on from graduate school), and said hello to new lab mates (Cara took over Cliff’s project; Gwynne started her post-doc; Tyler, Jay, and Max all joined the lab as undergraduate researchers and research assistants). In addition to COVID and personnel changes, I had orthopedic surgery that took me away from work for a little under a month.
But somehow, despite the challenges and changes, we managed to make progress on several research projects. Below, I present a partial reporting of the Garden Ecology Lab year in review for 2020. Besides each project heading is the name of the project lead(s).
1) Garden Bees of Portland (Gail & Isabella):Jason Gibbs’ group from the University of Manitoba provided final determinations for a particularly difficult group of bees to identify: the Lasioglossum sweat bees. In addition, Lincoln (Linc) Best provided determinations for garden bees collected in 2019. Isabella is entering in some of our last remaining specimens, and I am working through the database of over 2,700 collected specimens to ‘clean’ the data and double check data entry against specimens in hand. There are a few specimens that need to be re-examined by Linc, now that we have determinations from the University of Manitoba, the American Museum of Natural History (Sarah Kornbluth), and a graduate of Jim River’s lab (Gabe Foote).
Altogether, we collected between 76 and 84 species of bee across a combined acreage of 13.2 acres (sum total acreage of 25 gardens). The low end estimate conservatively assumes that each unique morphospecies (i.e. Sphecodes sp. 1 and Sphecodes sp. 2) are a single species, whereas the high end estimate assumes that each is a unique species. A few noteworthy specimens:
We collected one specimen of Pseudoanthidum nanum, which is a non-native species to our area, which seems to be establishing and spreading in Portland. Stefanie Steele from Portland State University is writing a note on this apparent introduction, and is using data associated with our single specimen in her paper.
We collected one specimen of Lasioglossum nr. cordleyi which might or might not be a new species. The notation nr. cordleyi means that this specimen looks similar to L. cordleyi, but that the morphology of this specimen is different enough than the normal ‘type’ for this species, that it catches your attention. Jason Gibbs’ group is retaining that specimen. Further study will be needed to determine if it is indeed a new species, or not.
Some of the species we collected (as well as their ecological characteristics) suggest that gardens might be healthy habitat for bees. For example, we collected 72 specimens of Panurginus atriceps, which is a ground-nesting, spring-flying bee. Previous studies of garden bee fauna found ground-nesting and spring-flying bees to be relatively rare. We found them to be surprisingly (but relatively) common in our collections. We also collected seven putative species and 23 specimens of Sphecodes bees. This type of bee is a social parasite that does not collect nectar or pollen or construct a nest for their brood. Instead, they take advantage of the hard work of other bee species, by laying their eggs in the nest of another female. Parasitic bees are often used as bioindicators of habitat health. They would not be present on a site, unless the site also supported their obligate hosts.
We collected two species of bee that are listed on the IUCN red list for threatened and endangered species: Bombus fervidus (18 specimens) and Bombus caliginosus (10 specimens). I am not yet sure if their presence in urban gardens suggests that these species are recovering, that these species might be urban-associates that would be expected to thrive in urban gardens, and/or if gardens might represent particularly good habitat for these species.
In 2021, I *hope* that I can complete gathering data for this study, so that I can begin to analyze data and write. I hope to make it out to every garden, one last time, to finalize garden maps that will be used to calculate the area allotted to ornamental plants, edible plants, hardscape, and unmanaged areas. Aaron has already mapped out the landscape surrounding each garden at radii of 500 and 1000 meters. Together, these data will be used to understand whether/how garden composition and the surrounding landscape interact to influence bee species richness.
OLYMPUS DIGITAL CAMERA
Gail collecting bees off of flowers, using an insect aspirator (left). A wildflower meadow in one of our largest gardens (center). Some of the over 2,000 specimens we collected, and Isabella pinned and labelled.
2) Native Plants and Pollinators (Aaron Anderson): In February, Aaron successfully defended his dissertation proposal and passed his oral examination, and thus advanced to Ph.D. candidacy!! Since that time, he has been busy sorting, identifying, and counting three years’ of insect samples from his 140 study plots, representing five replicates plots of 23 native plants, four ornamental plants, and a control ~ a task that he finished two weeks ago! His bees have been identified to species by Linc. Aaron has identified the thousands of other insects in his samples to the taxonomic level of family. He is working through analysis of his massive data set, and is simultaneously working on two manuscripts: one focused on just the bees and the other covering all other insects. We plan to turn the key points of these two chapters into an infographic that can be used by gardeners and green industry professionals, to select native plants that support an abundant and diverse assemblage of beneficial insects.
Aaron recently submitted the first paper from his dissertation for publication consideration, to the journal HortTechnology ~ and it was accepted, pending revisions! This paper reports on his survey of gardeners’ impressions of the aesthetic value of his study plants, and includes five specific recommendations for native wildflowers that Pacific Northwest nurseries might consider growing and marketing as pollinator plants (e.g. Gilia capitata, Clarkia amoena, Eschscholzia californica, Madia elegans, and Sidalcea asprella virgata). These plants all fell within the ‘sweet spot’ of being attractive to both pollinators and to gardeners.
Aaron’s plots at the NWREC station remain in place. Although we are through collecting data for Aaron’s study, I am applying for grant funding to study how plant traits ~ both the reward that plants offer pollinators and the displays that they use to attract pollinators ~ change with plant breeding for specific aesthetic traits, and whether/how these changes affect pollinator visitation. We also hope to study how highly attractive pollinator plants function in mixed plantings and in garden settings.
Aaron and Lucas measuring plots in year one (left); Douglas Aster, one of Aaron’s most attractive plants for bees (center); Oregon sunshine was less attractive to bees than we had expected.
3) Bees on Native Plants and Native Cultivars (Jen Hayes):
Jen successfully completed her first field season of research, which is a monumental accomplishment during this time of COVID restrictions on our work. In early 2020, Jen finalized her list of study plants, which included one native species and 1-2 hybrids or native cultivars. This, in and of itself, was a huge accomplishment. Although we started with a much broader list of potential study plants, so many native plants did not have native cultivars or appropriate hybrids available for sale.
Jen’s study plants, which include one native (top photo in each group) and 1-2 native cultivars or native hybrids.
Once Jen and her crew put the plants in the ground, a new set of challenges emerged. For example the native yarrow emerged with pink flowers, which was a clear signal that these plants were not true natives. In addition, the Sidalcea cultivars that Jen and her crew planted came up looking different than the Sidalcea native. This sent Jen on a journey to the OSU Herbarium, where she learned that the Willamette Valley’s native Sidalcea malviflora has been reclassified as Sidalcea asprella, and that the cultivars we purchased were hybrids of Sidalcea malviflora (native to SW Oregon and California). This all suggests a need to work with local nurseries and/or growers of native plants, to see whether or not there needs to be or can be standards for sale of native plants. Should native species and native cultivars be verified or share provenance? Should gardeners be asking for this information? I don’t know, but I think that they’re important questions to consider.
With one field season’s worth of data in hand, the native cultivars were more attractive to all bees (with overall patterns being driven by the abundance of the European honey bee) for all floral sets, except California poppy. When we excluded honey bees from the analysis, to look at (mostly) native bees, no clear pattern of visitation on native plants versus native cultivars emerged. Native California poppy was most attractive to native bees. But, native cultivars of Sidalcea were more attractive to native bees (keeping in mind that in 2020, our native cultivars were not cultivars of our regionally appropriate native plant). For all other plants, there was no difference. We look forward to collecting additional data in 2021 and 2022, to see if the lack of difference in bee visits to native plants versus native cultivars holds up. Particularly for the perennials, we are finding that bee visits change so much from year to year, as the plant becomes established.
Jen, pre-COVID times, discussing her research at the Urban Ecology Research Consortium conference (left). On every study plant, Jen takes data on corolla width and depth, as well as nectar tube length (center). Jen’s study site, with California poppy in the foreground, and a cultivar of California poppy towards the back (right).
4) Garden Microbes in Soil and on Skin (Dr. Gwynne Mhuireach): Dr. Mhuireach successfully recruited 40 gardeners to participate in this study: 20 from western Oregon and 20 from the high desert. She has received and processed all soil samples and all skin swab samples for PCR (genotyping), which will be used to infer the diversity and identity of the soil microbial community in garden soils and on gardeners’ skin. She has also received survey responses from all study participants, so that she can characterize gardeners’ crop types, time in the garden, and gardening practices (e.g. organic, conventional, or mixed).
Dr. Mhuireach then sent me the soil samples, so that I could process them for submission to OSU’s Soil Health Lab. The Soil Health Lab is currently performing the chemical and physical analyses on each soil sample, so that we can determine if there is any relationship between soil characteristics, gardening region (e.g. western Oregon or high desert), crop choices, management practices, and the microbes that can be found in garden soils and/or on gardeners’ skin. Gwynne just received the first data back from the PCR analyses ~ and we can’t wait to share some of the intriguing findings with you, after we’ve had some time to process and digest the data!
Because of COVID-19 lab closures, we are a bit behind where we had hoped to be at this point. We anticipate receiving all data from each service lab by the end of January or in early February. You can read more about Gwynne’s project, here.
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Beyond these four studies, Tyler started his BioResource Research project (costs and yield of container grown and intercropped tomotoes), and Isabella worked on her thesis (parasitoids in Portland area gardens). We also collaborated with OSU Computer Science students to turn a database of first frost / last freeze dates that Angelee compiled, into a web-based app (the app is still in beta-testing, but we hope to release it, soon!). I will detail those studies, in another post. But for now, I’m getting excited for the smell of carnitas that is filling the house, and that will go on top of the New Years’ nachos that will help us ring in 2021! I hope that you all have a very Happy New Year, and that 2021 brings health, and happiness, and joy to all.
Our colleague, Brooke Edmunds, was kind enough to shoot and edit this short video on two of our current lab projects: Jen Hayes’ study of native plants and nativars and Tyler Spofford’s study of the economic costs and benefits of growing vegetables in bucket gardens.
As we near the end of our 2020 field season, stay tuned for research updates.
What’s the first thing people see when approaching a house? The parking strip. What is often the ugliest, most barren part of a yard? The parking strip!
The parking strip, often called a “Hell Strip”, is a tough landscaping
challenge. Narrowly linear, sun-baked, hard to water, often compacted, subject
to foot, dog and other traffic…what self-respecting plant would want to grow
there?
This is why parking strip “landscaping” tends to default to lawn, mulch, or gravel.
But there’s another option. For every habitat there are plants to match,
so if you want a garden in your hell strip, choose plants that LIKE it hot and
dry, and are compact in size. Careful design and plant selection can result in
a parking strip that is a beautiful asset, rather than a barren wasteland.
As a bonus, many plants that are suitable for planting in a parking strip are also great for pollinators. There are many Oregon native plants that can thrive in such conditions, and since native plants are generally best for pollinators, why not dedicate your parking strip to growing mostly native plants in a beautiful pollinator garden?
Tips for Success
Before making any parking strip plans, be sure to check with your local government (the owner of the parking strip) for any regulations or requirements you need to take into account.
Provide a paved landing or path for exiting cars.
Don’t obscure utility covers with plants.
Before planting, loosen the soil and dig in compost. It can be worth spending a year or two improving the soil, if it is very bad.
Plant in fall if possible, to give plants all winter to grow strong roots before having to cope with summer heat and dry.
Be patient – it may take some trial and error to find the best plants for your parking strip.
Pollinator syndromes are the characteristics or traits of a flower that appeal to a particular pollinator. These traits often help pollinators locate flowers and the resources (e.g. pollen or nectar) that the flowers have to offer.
Syndromes include bloom color, the presence of nectar guides, scents, nectar, pollen, and flower shapes. We can use these traits to predict what pollinators might be attracted to certain flowers or we can use these tools to guide us to pick the right plant for the right pollinator!
Bees, for example, are most attracted to flowers that have white, yellow, blue, or ultra-violet blooms.
Blue Flax (Linum lewissii)
Male long-horned bee on a white bindweed flower
Orange bumblebee (Bombus sp.) on a sunflower
Pollinator Syndromes for Bees & Butterflies
Table adapted from the North American Pollinator Protection Campaign
Trait
Bees
Butterflies
Color
White, yellow, blue, UV
Red, purple
Nectar Guides
Present
Present
Odor
Fresh, mild, pleasant
Faint but fresh
Nectar
Usually present
Ample, deeply hidden
Pollen
Limited; often sticky or scented
Limited
Flower Shape
Shallow; with landing platform, tubular
Narrow tube with long spur; wide landing pad
What are nectar guides?
Nectar guides are visual cues, such as patterns or darker colors in the center of a flower, that lead pollinators to nectar or pollen. These cues are beneficial to plants and their pollinators because they can reduce flower handling time, which allows bees to visit more flowers and transfer more pollen in a shorter amount of time.
Northern Blue Flag Iris (Iris versicolor).
The petals (yellow arrow) and sepals (red arrow) both have dark purple nectar guides. The yellow portion of the sepals may also be a nectar guide!
Image courtesy of Mike LeValley and the Isabella Conservation District Environmental Education Program
While the iris’s nectar guides are visible to humans and their pollinators, this is not always the case. Some flowers have nectar guides only visible in ultra-violet light. The video below shows how different flowers look to us (visible light), and simulates what the flowers look like to butterflies (red, green blue, and UV) and to bees (green, blue, UV).
What about pinks and purples?
Red-flowering currant (Ribes sanguineum)
It’s not uncommon to see bees visiting flowers that are colors outside of their typical pollinator syndromes. In the spring in Oregon, we see bees visiting red-flowering currants, many pink and magenta rhododendrons, plum blossoms, and cherry blossoms. Lavender, catnip, and other mint-family plants too are common on pollinator planting lists, but tend to have purple flowers.
Pollinator syndromes can help us understand these anomalies. These flowers may appear differently in ultraviolet light or may have strong nectar guides that encourage bees to visit them, despite how they look to us. Alternatively, these flowers might have rich reserves of pollen and nectar that draw bee visits.
How else do we know if a flower is a good choice for bees?
Many people have developed plant lists based on personal observations, so there are many pollinator plant lists available to choose plants from. Many nurseries include pollinator attraction information with their planting guidelines too. While these are often based on anecdotal evidence, many researchers (including Aaron and I) are working to provide empirical evidence for plant selections.
To find native plants to attract bees and other pollinators, I recommend starting your plant selections by checking out your local NRCS Plant Materials program.
As an ecologist who studies garden systems, the increasing use of native plants in urban and suburban landscaping is exciting to me (see lab member Signe Danler’s great blog post on “ecological gardening”). Unfortunately, there are still many challenges associated with growing the adoption of native plants by home gardeners, with the largest barrier simply being the lack of availability of these species. I have noticed this barrier when giving talks to the public – many home gardeners are interested in gardening with high-ecological value native plants, but don’t know where to purchase them. These anecdotal observations are backed up by peer-reviewed literature, as several studies that have investigated the use of native plants in urban landscapes identified availability as one of the major barriers to adoption.
So, if you are a gardener in Oregon interested in gardening with native plants, where do you start? The good news is that native plants are available! Most big box stores (like Home Depot) have few to no native plants. One option is to go to a large, diverse nursery, like Portland Nursery or Garland Nursery in Corvallis. Besides perusing the selection of native plants they do stock, you can always ask them if they are able to stock a native plant you are interested in. These nurseries generally have contacts with a variety of growers, and demonstrating demand for native plants may lead to nurseries stocking more of these species on the shelf.
But what if you don’t have a specific native plant in mind, or what if you are new to the native plant world? Your best bet is to go to a specialty native plant nursery. Luckily, in Oregon there are a variety of native plant growers throughout the state. Below is a (non-comprehensive) list of some of the retail options. Keep in mind that some of these nurseries grow/stock a wide variety of species, while others specialize in plants of a certain region of the state or in a certain type of plant (think trees, or shrubs). I did not include nurseries that are primarily wholesale operations.
You can find more information on the Oregon Flora Project’s website, where they have a tool that lists Oregon native plant nurseries, as well as a list of what each grower stocks.
Finally, another great source of native plants are native plant sales! Many Master Gardener chapters and many soil and water conservation districts put on native plant sales in the spring. Here are a few, but check with these organizations in your county and see if they have sales scheduled!
As many of you may know at this point, Aaron Anderson and Jen Hayes are conducting some amazing research regarding Oregon native plants and their pollinator attractiveness. If you haven’t had the chance to read about their research yet, check out Aaron’s here and Jens here. While those two are producing data to determine the ecological benefits derived from some of our wildflowers, I chose to go down a more selfish route and see what our native plants can do for me. . .forget the bees. Below I have compiled a list of ethnobotanical uses for 6 of the 23 Willamette Valley wildflowers included in Aarons research – California Poppy, Camas, Pearly Everlasting, Oregon Iris, Western Red Columbine, and Goldenrod (my favorite).
Before you read any further, be aware that I am not an expert in wildcraft, ethnobotany, or herbalism. Never ingest the parts of any plant without being absolutely sure of its effects on the human body. Think of this more as a jumping-off point for your own research rather than any sort of guide or expert recommendation.
California Poppy –Escholzia californica:
Courtesy of Decker Seeds
The California Poppy – the ubiquitous orange herald of summer can do significantly more for you than just adding a pop of color to your yard or garden. E. californica can also be used as a medicine or candy! The flower itself is high in carotenoids and slightly sweet, the whole thing can be eaten raw as a candy-like treat. The ground roots and sap of the plant can be made into tinctures or infusions and be taken as a sedative, pain reliever, and muscle relaxer. California Poppy has been used by herbal practitioners as a “safe and gentle sedative for hyperactive children”. Maybe because they had too much poppy candy earlier in the day.
Camas – Camassia leichtlinii:
Courtesy of Euro Bulb
Courtesy of Honest Food
Camas is perhaps one of the best known plants on this list for its very popular edible bulb. The bulb is the most useful part of the plant and can be prepared in a few different ways. The two most popular are roasting and steaming. The roasted bulb gives off a flavor similar to a potato with a little hint of sweetness. Frying or mashing the bulb after the roasting are also common options to expand the flavor. Steaming camas bulbs is another popular practice which results in a food not unlike an onion. They are gelatinous and rich in complex carbohydrates, a fully browned camas bulb is just as delicious as any caramelized onion.
Pearly Everlasting – Anaphalis margaritacea:
Courtesy of Southern Living
Pearly Everlasting, a sweet little flower that has always reminded me a bit of a brilliant white star with a bright yellow center. These little flowers could also be a star of your ethnobotanical handbook considering how useful they are! The slender green leaves can be eaten as a normal green once they have been cooked a bit, perhaps by way of steaming or sautéing. A. margaritacea also offers a whole pallet of dyes all from one plant, depending on the concentration of each, it can provide shades of yellow, green, and brown. Pearly Everlasting can be employed as treatment for a whole range of ailments. The whole plant is filled with metabolites which can act as an anodyne, antiseptic, and sedative. Internally, it can also be used to treat diarrhea, dysentery, and some pulmonary affiliations. Externally, a poultice of the whole plant can be used to alleviate pain from burns, sores, ulcers, and bruises.
Oregon Iris – Iris tenax:
Courtesy of Katen Fahey
Courtesy of Mt. Pisgah Arboretum
Oregon Iris is well known and celebrated for its floral beauty, but its grass-like leaves are often overlooked despite their usefulness. The long and immensely durable leaves can be used to make ropes or baskets. The 19th century botanist David Douglas once described Iris tenax’s leaves as “. . .in point of strength it will hold the strongest bullock and is not thicker than the little finger”. Like any craft, basket-weaving requires practice and learning, however the unique texture and color of the leaves are bound to make the product stand out among the rest.
Courtesy of East Tennessee Wildflowers
Western Red Columbine – Aquilegia formosa:
The number of uses associated with Aquilegia formosa practically matches the number of bright red petals surrounding its cascading stamens. In terms of edibility, Western Red Columbine boasts edible leaves when boiled and a sweet nectary treat from the flowers themselves, but you have to share with the hummingbirds. Medicinally, treatments can be found from the roots, seeds, and leaves. The mashed roots can be used to relieve aching pains, for diarrhea, to counteract dizziness, and stomachaches. The chewed leaves can be used to alleviate sore throats and calm and upset stomach. Finally, a paste made from mashed seeds can be applied to the scalp to kill lice!
Goldenrod – Solidago canadensis:
Courtesy of USDA Plant Guide
Although sometimes considered cumbersome due to its amazing ability to spread, Goldenrod is one of the Pacific Northwest’s most diversely useful plants. It offers medicinal properties from its internal metabolites, edible roots and seeds, and of course Goldenrod’s signature pigmentation can be harnessed for dying. Infusions made from the flowers can offer relief from a variety of ailments, fever, flu, diarrhea, and sore throats are just some. Roots are commonly eaten smoked and seeds can be eaten roasted or raw. Finally, the flowers can bring a beautiful golden hue to any natural fiber that needs dying, just with a simple soak in warm water.
Natives vs Nativars Recent studies report an increase in consumer demand for native plants, largely due to their benefits to bees and other pollinators. This interest has provided the nursery industry with an interesting labelling opportunity. If you walk into a large garden center, you find many plant pots labelled as “native” or “pollinator friendly”. Some of these plants include cultivated varieties of wild native plant species, called “nativars”. While many studies confirm the value of native plants to pollinators, we do not yet understand if nativars provide the same resources to their visitors.
An Echinacea Example Above are three purple cone flower (Echinacea purpurea) plants: on the top is the wild type, in the middle is a nativar ‘Maxima’, and on the bottom is another nativar ‘Secret Passion’. In some cases, like ‘Secret Passion’s double flower, there is an obvious difference between a nativar and a wild type that might make it less attractive to insect visitors. Since we can’t see the disc flowers (the tiny flowers in the center of daisy family plants), we might assume that ‘Secret Passion’ may be more difficult for pollinators to visit. The floral traits displayed by ‘Maxima’ seem similar to the wild type, but it might produce less pollen or nectar, causing bees to pass over it.
Unless we actually observe pollinator visitation and measure floral traits and nectar, we can’t assume that natives and nativars are equal in their value to pollinators.
Nativar Research One study looking at the difference between native species and their nativar counterparts has come out of the University of Vermont (my alma mater!). A citizen science effort started by the Chicago Botanic Garden is also currently ongoing. My Master’s thesis will be the first to use a sample of plants specific to the Pacific Northwest. We have selected 8 plants that are native to Oregon’s Willamette Valley and had 1-2 nativars available. These plants have shown a range of attractiveness to pollinators (low, medium, or high) based on Aaron’s research. We are including plants with low attractiveness because it’s possible that a nativar may have a characteristic that makes it more attractive, such as a larger flower or higher nectar content.
This example of a Randomized Complete Block design shows 2 garden beds containing a native species (California Poppy and Camas) and their nativar pairs (a yellow poppy nativar and a white Camas nativar).
Experimental Design We have four garden beds in our study, and each bed contains at least one planting of each native species and their nativar counterpart(s). This kind of design is called a “Randomized Complete Block” (RCB). The RCB has two main components: “blocks”, which in our case are garden beds, and “treatments”, which are our different plant species. Above I have drawn a simplified RCB using two of our plants: Camas and California poppy. The bamboo stakes outline each plot and have attached metal tags that label the plants.
We planted our seeds and bulbs in November and will plant out 4″ starts of the other plants in early Spring. Look out for my spring and summer updates to see how these plots progress from mulch and bamboo stakes to four garden beds full of flowers and buzzing insects!
For my dissertation research, I am studying which native Willamette Valley wildflowers are most visited by pollinators and natural enemies for use in home gardens and urban landscaping. I’ve previously shared preliminary results from my field study on our blog, namely pollinator abundance and richness. For a refresher, here are summaries from 2017, 2018, and 2019.
Initial survey
Determining which of these flowers are most attractive to insects is only half of the equation — I also want flowers that are attractive to gardeners. To investigate this I developed two surveys — thanks to anyone reading who took them! The first simply asked gardeners to rank the aesthetic appeal of my study plants, as well as how likely they would be to utilize them in their home gardens. This allowed me to get a baseline understanding of how appealing these flowers are for use in home gardens and landscaping.
As you can see in the figure below, many of the plants most visited by bees (highlighted in orange) were the least attractive to gardeners (Fig. 1), while plants gardeners liked the most (e.g. Iris, Columbine) were hardly visited by bees. However, its notable that many of these native wildflowers ranked around a four on a 1-5 scale, showing that these flowers do have a high potential appeal for use in landscaping!
Figure 1: Gardener ranked aesthetic appeal of study flowers on a scale of 1-5. Orange bars note plants that were consistently highly visited pollinator plants. N=587
Follow-up survey
The follow-up survey consisted of a subset of ten flowers most visited by bees, and again asked respondents to rank the aesthetic appeal and likelihood of planting for each of these flower species. Then, they were shown facts about and images of bees that visit each flower species, and asked whether they viewed each plant species more favorably, less favorably, or the same. Finally, they were asked to re-rank how attractive they found the flower species and how likely they would be to use the species in their garden, both on a scale of 1-5.
Gardener acceptance
This second survey showed a remarkable increase in gardener acceptance of pollinator friendly native plants after being educated on plant-pollinator associations. Over 80% of respondents stated that they viewed Clarkia amoena as more attractive after gain, and over 60% of respondents viewed Phacelia heterophylla, Madia elegans, and Gilia capitata as more attractive (Fig. 2).
Figure 2: Percent of respondents viewing flower species as more attractive after learning about pollinator associations. N=184.
Likelihood of planting
After learning about the benefits these flowers provide to pollinators, gardeners were also more likely to plant all ten flower species (Fig. 3). Notably, they were 40% more likely to plant Phacelia heterophylla, (a species that ranked as the least aesthetically appealing overall in the first survey). As a whole, they were also over 20% more likely to plant Solidago canadensis, Clarkia amoena. Similar increases were also observed in likelihood of planting Oreganum vulgare and Nepeta cataria. Many of the plants that showed a smaller percent change are species that started out with a higher aesthetic appeal (e.g. Gillia capitata, Lavendula intermedia, Aster subspicatus), meaning gardeners were already very likely to include these plants in their home garden before learning about the ecological benefits they provide.
Figure 3: Percent change in respondent’s likelihood of planting each top pollinator flower after learning about the pollinators associated with each. N=184
Ecological beauty
What does this all mean? This suggests that although native plants are frequently denounced as being less attractive than showy garden species, many home gardeners are still willing to use native flowers in their landscaping. Additionally, this lends credence to the concept of “ecological beauty” – that many gardeners are willing to utilize plants that will increase the habitat value and wildlife diversity in their yards.
