Five Scientific Studies that Changed the Way I Think About Gardens: Part 1

[Preface: For the past few years, I have written a column for the Hardy Plant Society of Oregon’s (HPSO) Quarterly Magazine. It has been a wonderful experience, as the HPSO provides excellent editorial assistance. Below, I share my most recent article for the HPSO Quarterly, and thank Eloise Morgan and her team for helping to improve and elevate my writing.]

I spend my nights thinking about gardens: not about the plants that I want to purchase or the crops that I want to plant. Instead, I puzzle over how to study a system that is incredibly variable (from person to person, or even in the same person’s garden from year to year) and complex (with more plant species than just about any other system that has been studied). Gardens are both wild and managed, and unlike other systems I have worked, it is impossible to divorce human behavior from the ecology and evolution of the garden.

In this series, I wanted to share five scientific studies that have had a large role in shaping how I think about gardens. Because of space limitations, I will share the first study in this article. I will wrap up the remaining four studies, in subsequent issues. The five studies are:

Simberloff and Wilson (1969). This study commenced 54 years ago, and yet remains a ‘must read’ for any ecology student. In 1966, Dan Simberloff and Ed Wilson selected six small mangrove islands off the coast of Florida. The islands varied in distance from the mainland coast, from near to far (Figure 1a), as well as size, from small to large (Figure 1b)

Figure 1. In Simberloff and Wilson’s experiment, they selected mangrove islands that varied in their (a) distance from the mainland (the coastline of Florida) and (b) their size. Attribution: Hdelucalowell15 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Simberloff and Wilson constructed a scaffold that encircled the edge of each island, covered the scaffold with a tarp, and then proceeded to ‘defaunate’ each island with methyl bromide pesticide. In other words, they killed every arthropod on the islands. After removing their ‘death tents’, and over the course of the next year, they carefully monitored, cataloged, and counted every arthropod that arrived and survived on each island. What they discovered was formulated into the ‘Theory of Island Biogeography’, or a theory about how organisms colonize new habitat, and assemble into a biological community.

They found that islands that were closer to the mainland coast of Florida were colonized earlier, and accumulated species faster, compared to islands that were farther (Figure 2). They also found that species would accumulate on each island, over time, until a maximum peak is reached (not shown). Then, the number of species would begin to drop, as ecological interactions (such as competition for food) would allow some species to prosper, while others went locally extinct. They found that smaller islands were more prone to species extinctions, than larger islands (Figure 2).

Figure 2. Island size (small or large) and distance from the mainland coast (near or far) infuenced the dynamics of species colonization and extinctions on mangrove islands. Image Source: https://commons.wikimedia.org/wiki/File:Island-biogeography.jpg#file

Size, distance, age: those are the three things that Simberloff and Wilson predicted would govern the diversity and assembly of organisms within a habitat.

My first faculty position was at Fordham University in New York City, where I studied pollinators in 18 community gardens in Harlem and in the Bronx. During the course of this study, I was inspired by Simberloff and Wilson. I could not help but see the 600+ community gardens that dot the landscape of New York City as islands of green in a sea of concrete.

We expected that gardens that had been long-established would have more pollinator species than newer gardens. We expected that larger gardens would host more pollinator species than smaller gardens. And, we expected that gardens that were closer to ‘mainland’ sources of pollinators, such as Central Park or the New York Botanical Garden, would have more species of pollinator than those that were distant.

We were wrong on two out of three predictions (Matteson and Langellotto 2010). Larger gardens had more pollinator species than smaller gardens, but neither distance nor age had any impact. I was so disappointed that we did not find an effect of distance, or of garden age. I had visions of ‘revitalizing’ the Theory of Island Biogegraphy for urban landscapes, but it was not to be. If anything, our study suggested that the ‘sea of concrete’ was not exactly a wasteland, afterall. The street trees, potted plants, windowsill gardens, and patio gardens all provided resources for urban pollinators, even in one of the most densely populated and heavily developed cities in the world.

This study showed me that it will be much more difficult to track pollinator movements among urban gardens, than I had hoped. We tried to use a traditional mark-recpture approach (see Matteson and Langellotto 2012), but out of 476 marked butterflies we only found four in a garden other than which it was marked and released. We were searching for the ‘needle’ of small butterflies in the ‘haystack’ of the New York City landscape. My students tried to follow pollinators as they left our study gardens, and almost got hit by a car, as they were running across the street. We played around with the molecular markers of a few bumblebees (see Morath 2007), to see if there was evidence of genetic differentiation, but were stymied by a lack of reliable primers that could help us look for any genetic differences in bees from different gardens. And then I moved to the Willamette Valley, where gardens are islands of green in an ocean of green. Understanding what draws pollinators to particular gardens will be even more difficult in this landscape, where pollinators have so many other choices for finding nectar and pollen.

Based upon our initial results from our Portland Garden study (2017-2019), I think I have a new hypothesis as to what might draw pollinators to home and community gardens. Our second study year (2018) was characterized by a hot and dry summer. Our first sampling season was also dry, but the spring months were wet, and the summer was cooler. In 2018, we collected far more bees (abundance) and more types of bees (species) than we collected in 2017 or 2019. In 2018, the landscape of the Willamette Valley was toast! Almost all flowering plant materials seems to shut down photosynthesis, so that they could conserve pressure water that would otherwise escape through open stomates. In this type of situation, bees seemed to concentrate in home gardens, which seemed to be one of the few places where they could reliably find nectar and pollen.

If this is the case, gardens aren’t necessarily going to be an important source of floral resources across all years. In a good year, there should be other plants in bloom in the greater landscape that bees can use. But in a hot, dry year, gardens may become an even more important refuge for bees. Most gardeners provide irrigation, which extends the bloom season beyond what is natural in the valley. Or, gardeners select plants that can prosper and bloom without supplemental irrigation, such as goldenrod or Douglas aster. It’s important to note that, even in the hot, dry weather of 2018, we still collected more bees from gardens that used drip irrigation, rather than overhead sprinklers. I think that the overhead irrigation physically blocks bees from navigating through a garden, which lessens their abundance and diversity.

Ultimately, I hope that our studies can lead us to a more predictive model of the resource value of home gardens to pollinators. The goal isn’t necessarily to understand what gardeners should do to attract pollinators, but to describe the conditions where gardens become increasingly important to pollinator conservation. In addition, I’d love to describe the value of gardens, relative to other habitat types, to pollinators. And finally, I hope to better understand the direction and movement of pollinators between gardens and other habitat types.

 

Does Repeated, Lethal Sampling Contribute to Insect Declines?

Over the past few months, I have shared data on bees and other insects that we have collected from Portland-area gardens. For every garden insect we study (except for butterflies, which can be identified to species by sight), we use lethal collection methods. This is because most insects can only be identified to species after close examination under the microscope. In fact, some insects require dissection before we can get them to species.

Bombus sitkensis male, with abdomen dissected, in order to make a species-level identification.

It seems odd that we kill bees in order to help understand how we can build gardens that can help to conserve bees. By collecting and killing bees and other insects, what role were we playing in promoting insect decline? How do projects, such as our own as well as the Oregon Bee Atlas, factor into bee declines?

That’s an excellent question, and one that we often ask ourselves. When we collect bees, we work to make sure that we are not needlessly causing harm. For example, our pan traps are good for collecting small bees, but are not good at collecting larger bees, including reproductive queens. When we hand-collect bees, we avoid taking queen bees. In fact, of the 2,716 bees that we collected in 2017-2019, only three were queens. We limited our sampling frequency to three times per year, and limited our sampling effort to 10 minutes of hand-collecting time and six pan traps, per garden. Even with these precautions, we are still faced with the question: does our research, or the research of others who collect and kill insects, harm the very species we are trying to conserve?

Water pan traps, used to collect garden bees and other small, flying insects. Insects are attracted to the color. When they land in the soapy water, they break the surface tension, drown, and die.

To address this question, I turn to the scientific literature. Gezon and colleagues set up an experiment to see whether lethal sampling for bees using pan traps and netting (the same methods we use in our research) has negative effects on bee abundance or bee diversity. For five years, they sampled nine sites every two weeks during the flowering season. They compared bee abundance and bee diversity in these repeatedly-sampled sites, to metrics from 17 comparable sites that were only sampled once. They found no significant difference in bee capture rate, bee species richness, or bee abundance between sites that were sampled repeatedly versus those that were sampled once. When they partitioned bees according to nesting habit (e.g. cavity, soil, wood, etc.), social structure (e.g. eusocial or not), and body size (e.g. small, medium, and large bees) they also found no significant differences in bee capture rates of single-sample versus repeat-sampled sites. They did catch more pollen specialists in repeated-sample sites than in single sample sites. However, the magnitude of the effect was relatively small, and did not represent a large change in catch rate between single-sample versus repeat-sampled sites. I suspect that the authors caught more pollen specialists at their repeat-sampled sites, because pollen specialists are fairly rare in time and in space. They drastically increased their odds of intercepting a pollen specialist on their repeatedly-sampled sites.

Gezon and colleagues suggest a few hypotheses that could explain why increased sampling effort had no significant effect on bee abundance or diversity. First, they suggest that reducing bee populations by sampling could benefit the bees that remain, by reducing competition for limited resources. If this is the case, bee populations can compensate for some losses due to sampling, by increasing reproduction in the bees that remain behind. Second, they note that if bees were sampled after they have mated and laid eggs, the overall impact of removing a bee from via sampling will be fairly small. Finally, they note that most bees are solitary, and that most solitary bees have short flight seasons. In this case, sampling every two weeks may not result in bee declines, if researchers are effectively collecting a new species during each sampling event.

I can breathe a bit easier. The data suggests that our research is not immediately responsible for documented bee declines. Still, I know that I can personally do more to help protect bees in my own garden. Even though our lab group studies native plants, I have not yet planted Aster subspicatus (Douglas’ Aster) in my own garden. This will be my mission for 2020: to find and plant this gorgeous perennial at home. In 2018 and 2019, it bloomed from mid June through mid November at our study plots in Aurora, OR, with peak bloom (75% or more of the plant in bloom) lasting one month! And, from 2017-2019, it was always a top five plant for native bee abundance. I give this Pacific Northwest native plant my highest recommendation for home gardens! There are plants that attract more native bees, such as Phacelia heterophylla. But, no other plant that we studied offers the triple threat of beauty, bees, and longevity.

Douglas’ aster (Aster subspicatus) is currently my favorite garden plant for bees.

Native Plants and Pollinator Survey

Aaron Anderson is repeating his original survey on native plants and pollinators. This time, he is trying to understand how knowledge of a plant’s ecological function may alter impressions of native plants.

The survey takes about 25-30 minutes to complete. Folks who have taken the survey thus far have commented on how much they learned from taking the time to answer the questions.

If your time and interest allows, we would be extremely grateful if you could take the time to respond to this survey. The direct link to the survey is:

http://oregonstate.qualtrics.com/jfe/form/SV_9Alhv961rZX8Vs9

If you have friends or acquaintances who also might be interested in taking the survey, please feel free to share it with them.

A syrphid fly pays a visit to a California poppy at the North Willamette Research and Extension Center.

A bee visiting one of the Canada goldenrod plots in our Native Plant study.

Gilia capitata

Lotus unifoliolatus

PolliNation Podcast and Lab Update

If you love bees, and you have not yet subscribed to PolliNation, you’re missing out! OSU Professor and PolliNation podcast host, Andony Melathopolous, does a wonderful job assembling a diverse array of guests to talk all things pollinator.

Aaron Anderson recently joined Andony on episode 94 of thePolliNation podcast, to talk about his research on native plants, different insect groups, and gardeners.

Aaron talks about the 100+ study plots that he manages (two of which you can see, below), as well as which plants were most attractive to bees (such as the California poppy, on the left) versus those that were more attractive to gardeners (such as the Oregon iris, on the right).

In other news, our lab group has been very busy. All of the 2017 and 2018 bees from our garden pollinator study have been identified to species (unless they are truly recalcitrant to being ID’d to the level of species).  Gabe has been working with Lincoln Best to identify the 2018 bees.  The 2017 were verified by Sara Kornbluth, and provided a great reference collection against which we could compare the 2018 bees. Gabe has been a short-time member of our lab group, but his expertise has been a huge benefit to our program. He leaves us at the end of April to start field work in the College of Forestry. After that, he heads to UC Davis to do his Ph.D.

For the garden bee project, we have >50 verified species of bees collected from Portland-area gardens, with a few more at the morpho-species level. This summer will be our final year of collections.

This summer will also be Aaron’s final year of field work at the North Willamette Research and Extension Center. This final year will help to resolve some of the differences we saw between his 2017 and 2018 data set.

After two years of amazing assistance in the lab and in the field, Isabella has started an independent research project on campus. She has planted some of Aaron’s study plants in gardens on campus, and is looking to see if bee visitation and bee communities markedly change, when you take them out of single-species plantings (like Aaron is studying) and put them into a garden setting.

Mykl is working to write up his urban soils data for publication. We are also hoping to do a side publication, comparing the soil types that we’re finding in home gardens, and seeing how they align with the types of soils that nesting bees prefer.

Lauren is writing up her capstone paper, and is preparing to defend this term. She surveyed gardeners to try to understand how well they can identify bees from other insects, and how well they knew bee-friendly plants from those that offered few or no nectar/pollen resources to bees.

Signe is taking the data that we are collecting, and working our findings into the online Master Gardener course. The best part of our work is being able to see gardeners put some of our research-based recommendations into action. Signe plays a huge role in translating our work for the general public.

Angelee is a relatively new member of the lab. She comes to us from the OSU STEM Leaders program. She’s learning lab protocols and lending a hand on just about every project. She has been a joy to work with.

Lucas has moved on from the lab, but still helps us with remote data-basing work, on occasion. He was a joy to work with, and I feel lucky that he stuck with us for a few years.

This fall, Jen will be joining our group as a new M.S. student. We will also be close to launching the first course in the online Urban Agriculture certificate program, which is being spear-headed by Mykl. We should also be pushing out a few more papers from our garden work, to join our first concept paper on the value of urban garden bees to urban and peri-urban agriculture.

 

Plant of the Week: Douglas Aster (Revisited)

Image from: http://www.nwplants.com/

This entry is from Lucas Costner, an undergraduate horticulture major at Oregon State University.  It highlights one of the plants that Aaron Anderson is using in his research.

Original “Plant of the Week: Douglas Aster” post available here: http://blogs.oregonstate.edu/gardenecologylab/2017/11/07/plant-week-doulgas-aster/ 

 

Last November I took a look at a Pacific Northwest favorite, the Douglas aster (Symphyotrichum subspicatum (1)). What I didn’t know then was just how popular this species would be with the bees we had been sampling in the field. It turns out that while surveyed gardeners ranked Douglas aster 14 out of 27 in terms of attractiveness, based on the 2017 data it boasted the third highest number of bees (2). This means that it is the most attractive native perennial species for bees that we sampled, and the 2018 data shows this as well (3). Based on the gardeners’ ranking, however, which placed it in the bottom 50% of all the species we sampled, it also looks as though the Douglas aster is in need of some public relations help. 

It is my personal belief that it isn’t just the showiness of the blooms or the potential benefits to X, Y and Z that brings plants into our gardens, but rather the stories we tell about them. Familiarity after all is more than just recognition; it is also marked by appreciation and understanding. One of the stories we can tell through our work in the Garden Ecology Lab about Douglas aster is of its relationship with our native bees. As gardeners we are uniquely positioned to both benefit from and to be of service to these insects. 

Here are some of their “faces”: 

Long-horned Bees

Melissodes sp. 

The most common genus of bees collected from Douglas aster in the field, Melissodes are true summer and fall flyers, easily recognizable by their long antennae. These bees are solitary ground nesters, although they have been observed forming nesting aggregations in the soil (4). While we collected potentially five species of Melissodes in total, one species in particular, Melissodes microsticta, was especially common. Many Melissodes species are generalists, but can usually be found visiting members of the Asteraceae family (such as sunflowers and our Doulgas aster) because of their late season blooms.

 

Image from: https://odabeeguide.weebly.com/melissodes.html

Yellow-faced Bumblebee

Bombus vosnesenskii

The second most commonly collected visitor of Douglas aster, the yellow-faced bumblebee is really a remarkable native pollinator. While many native bees are considered solitary, bumble bees are social insects, with a queen and workers (4). Like non-native honeybees, they have been investigated for their potential as commercial pollinators, being used in greenhouse production (5). Isabella Messer wrote a post for the “Pollinator of the Week” series highlighting these ubiquitous bees that can be found here: http://blogs.oregonstate.edu/gardenecologylab/2017/08/29/pollinator-week-yellow-faced-bumble-bee/ 

 

Image from: https://odabeeguide.weebly.com/bombus-sp.html

Ligated Furrow Bee

Halictus ligatus

The third most commonly collected visitor of Douglas aster is the ligated furrow bee. Found throughout North America, Halictus ligatus is special amongst native pollinators (like the yellow-faced bumblebee) for its social nature (4). Sociality is rare amongst native bees, as it is in nature in general, but amongst the Halictus the situation is even more unique. This is because, unlike other social species, Halictus have been seen to switch back and forth between solitary and social behaviors over time as environmental conditions differ (4). Isabella wrote a post about these bees a while back for the “Pollinator of the Week” series that can be read here: http://blogs.oregonstate.edu/gardenecologylab/2018/04/30/pollinator-week-mining-bee/ 

 

Image from: https://odabeeguide.weebly.com/halictus.html

Virescent Green Metallic Bee

Agapostemon virescens

The fourth most commonly collected visitor of the Douglas aster is none other than my personal favorite, the virescent green metallic bee. These stunning bees are communal soil nesters and are members of the Halictidae family, cousins of the ligated furrow bee introduced above (4). I wrote a post about them for the “Pollinator of the Week” series last November that can be found here: http://blogs.oregonstate.edu/gardenecologylab/2017/11/13/pollinator-week-virescent-green-metallic-bee/ 

 

Image from: https://odabeeguide.weebly.com/agapostemon.html

In addition to these bees, we also collected striped-sweat bees (Agapostemon texanus/angelicus), brown-winged furrow bees (Halictus farinosus), metallic sweat bees (Lasioglossum sp.), and common little leaf-cutter bees (Megachile brevis). We also collected with a number of long-horned bees (Melissodes) that have yet to be identified to species. 

Walking the streets of Portland and seeing Douglas aster’s purple flowers still in bloom this late in October brings a smile to my face because it tells me that people are indeed planting this species. If only for its benefit to wildlife and pollinators in particular, that is still good news. As you may be able to tell from the information given above, we are still learning about these bee species while we are simultaneously working to save them — not just for future generations but for ourselves as well. Hopefully, by putting a “face” to the bees that visit and depend on these plants and our gardens, the bond that links us to them can be strengthened and our preference for them in our landscape enhanced. 

 

Sources: 

  1. Geraldine A. Allen 2012, Symphyotrichum subspicatum, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=88843, accessed on October 30, 2018.
  2. Langellotto, G. (2018, September 12). Do Gardeners Like the Same Flowers as Bees? [Blog post]. Retrieved from http://blogs.oregonstate.edu/gardenecologylab/2018/09/12/do-gardeners-like-the-same-flowers-as-bees/ 
  3. Anderson, A. (n.d.). First Look: Research Into Native Plants in the PNW Garden. Webinar. Retrieved from http://blogs.oregonstate.edu/gardenecologylab/2018/10/23/webinar-on-willamette-valley-native-plants-and-pollinators/ 
  4. Wilson, J. S., & Messinger Carril, O. (2016). The Bees In Your Backyard. Princeton, NJ: Princeton University Press.
  5. Dogterom, M. H., Matteoni, J. A., & Plowright, R. C. (1998). Pollination of Greenhouse Tomatoes by the North American Bombus vosnesenskii. Journal of Economic Entomology, 91(1), 71-75. doi:https://doi.org/10.1093/jee/91.1.71
  6. Oregon Department of Agriculture: Bee Pollinators of Oregon. (2016). Retrieved October 30, 2018, from https://odabeeguide.weebly.com 

Garden Bee Webinar

In case you missed the webinar on our garden bee research, I’ve embedded the video, below. The entire webinar is about an hour.

And, make sure to mark your calendars for Monday, October 22nd at 11am PST. Aaron Anderson will be presenting a FIRST LOOK webinar on his research on native plant-pollinator associations. Visit the hypertexted link, above, to register for this FREE webinar.

Aaron was sharing some of his latest data with me, just this past week. His data, collected at replicated field plots in Aurora, Oregon, echoes what we’ve seen in home garden sites around Oregon: for native bees, Douglas Aster was a top performer.

Pollinator Survey

Lauren Bennett, a Master’s student at OSU, is doing her capstone project on pollinators She has a short survey (10-15 minutes) on pollinators and pollinator plants.

If you could spare a few moments of your time, we would appreciate your participation in this study. More information this study can be accessed, by following the link, below.

http://oregonstate.qualtrics.com/jfe/form/SV_bw2OqokCObh83rv

FYI ~ this study was deemed ‘quality improvement / assessment’ and not ‘scholarly and journalistic’ by the OSU IRB. Thus, we do not need or have IRB oversight for this study.

 

First Bee List from Native Plant Study

We are so lucky that Lincoln Best has been in Oregon, supporting the work of the Oregon Bee Atlas. Linc was kind enough to take a look at Aaron’s bees, before going back to Canada. Aaron is currently taking a bit of time off, following his wedding this past weekend (Congratulations Aaron and Maura!). In everyone’s absence, I’m chomping at the bit to see what bees were identified from Aaron’s study of Willamette Valley native plants. So ~ for your reading pleasure, here is a preliminary list of bees collected from Aaron’s plant plots.

Aaron and Lucas in the native plant study site. You can see the 1m by 1 m plot in the foreground by Aaron, a second one near Lucas, and a few more in the distance.

A few things to note about this list:

  1. I give no mention of abundance of each bee species. Some specimens were caught many, many times off of a flowering plant species. Others were rare, and only caught once.
  2. This list is not all-inclusive. It’s Labor Day. I’m working. I got excited about the bees, and wanted to share. But, I am not carefully going through every small label.
  3. Some bees were only found on one or two flowering plant species ~ even though Aaron’s plots are all in the same 3 acre field (1X1m plots, with each plot separated from every other plot by 6 m).
  4. Yellow-faced bumblebees were collected off of most plants ~ so I am not listing them, below. I also did not look at the honey-bee plant associations.
  5. Linc dissected male genitalia (yes ~ that is how you need to ID some bees to species), and found FOUR Bombus calignosus (all associated with lavender)~ a vulnerable species on the IUCN Red List.
  6. We also have Bombus fervidus, another species on the IUCN Red List (Vulnerable) on lavender, Salvia, and Gilia.

I’ll leave it to Aaron to make a rigorous accounting of bee-flower associations. But for now . . . on this holiday weekend, I was too excited to not take a peek and share initial findings with all o fyou.

Nepeta (non-native comparitor)

Oregano (non-native comparitor)

Salvia (non-native comparitor)

Lavender (non-native comparitor)

Phacelia (native)

Clarkia (native)

Goldenrod (native)

California Poppy (native)

Doug Aster (native)

Oregon Iris (native)

Gilia capitata (native)

Oregon Sunshine

Madia (native)

Sidalcia (native)

Yarrow (native)

Pearly Everlasting (native)

Urban Garden Soils Study Update

It has been a busy summer in the Garden Ecology Lab!

  • Mykl Nelson successfully defended his thesis on urban garden soils, and graduated with a M.S. in Horticulture this past June.
  • Gail, Aaron, and Mykl all shared their research results with Master Gardeners, at the recent Growing Gardeners conference.
  • Aaron continues his fieldwork, documenting the attractiveness of several Willamette Valley native plants to pollinators. You can find his full list of plants here.
  • Aaron launched the survey part of his research, to document the attractiveness of these same plants to gardeners. If you would like to participate, you can find our recruitment letter, here.
  • Gail and Isabella continue to sample insects on a monthly basis, from 24 Portland area gardens. Our July sample has been pushed to the week of July 30th, because Gail was invited to serve as a panelist on a USDA grant panel. Sampling takes four long days ~ made all the more difficult by Portland’s heat wave. But, sampling during the heat wave will be interesting. Do garden habitats become even more important to bees, when the heat dries up forage in natural and wild habitats? We shall see.
  • Bees from our 2017 sampling effort have been pinned, labelled, and sent to the American Museum of Natural History for expert identification. Thank you to the Oregon Master Gardener Association for a $500 grant to help pay for the expert bee identification.

Today, I’m packing field supplies and clothes for the July 30-August 2nd garden bee sampling effort. It seemed like a good time to provide an update on our garden soils work. I wrote this article for the Hardy Plant Society of Oregon quarterly magazine. I thought that others who are interested in garden ecology might be interested in seeing an update on this work. We are currently working on a manuscript of Mykl’s research, for submission to the journal Urban Ecosystems. In the meantime, some of the highlights can be found below.

**********************

Despite the popularity of urban agriculture, we know virtually nothing about urban agricultural soils, including residential vegetable gardens. We thus studied urban garden soils to get a sense of the characteristics of residential-scale, urban agricultural soils in western Oregon. Last year, we took soil samples from 27 vegetable gardens in Corvallis and Portland, and tested for differences between garden sites based upon bed-type (e.g. raised beds versus in-ground beds). All gardens were managed by certified Extension Master Gardeners.

If you have taken a Master Gardener soils class, perhaps you have heard the soil management mantra ‘just add organic matter!’. This mantra comes from the idea that adding more organic matter (OM) can improve soil tilth and nutrition. However, this mantra was derived from research in large-scale farming systems, where farmers often struggle to raise their soil OM by even 1%, across tens or hundreds of acres of crop production.

We found that nearly every garden that we sampled had an excess of OM (Table 1). Soil management guidelines suggest that farmers should aim for 3-6% soil OM. Across all of our garden study sites, vegetable garden soils were on average 13% OM, by volume. Raised beds were significantly over-enriched in organic matter (15% OM, on average), compared to in-ground beds (10% OM, on average). To put it another way, Master Gardener-tended vegetable gardens were over-enriched in OM by 2-5 times the recommended level!

This excess in organic matter likely contributed to excessive levels of other soil parameters. For example, most garden study sites were above recommended levels for electrical conductivity (a measure of soil ‘salts’). All gardens were above recommended levels for sulfur (S), phosphorus (P), calcium (Ca), and magnesium (Mg) (Table 1). Only nitrogen (N), potassium (K), and boron (B) were generally within recommended levels (Table 1).

Table 1. Percent of garden study sites that were within, above, and below recommended ranges for various soil parameters. OM: organic matter. EC: electrical conductivity. N: nitrogen. S: sulfur. P: phosphorus. K: potassium. Ca: calcium. Mg: magnesium. B: boron.

Soil Parameter Percent of Garden Study Sites
Within Recommended Range Above Recommended range Below Recommended Range
OM 6% 94% 0%
EC 18% 82% 0%
N 70% 30% 0%
S 0% 100% 0%
P 0% 100% 0%
K 73% 24% 3%
Ca 0% 100% 0%
Mg 0% 100% 0%
B 42% 3% 55%

The excessive organic matter in residential-scale garden soils makes sense, when considered in the context of garden size. In small garden plots, gardeners can easily over-apply products which have been recommended for successful, large-scale, agricultural production. It is easy to imagine that the over-abundance of organic matter in soils results from large amounts of compost added to a relatively small area.

Our results point to the importance of conducting periodic soil tests in garden soils. Instead of ‘just adding organic matter’, gardeners need to understand where they are starting from, before adding amendments and fertilizers to their soil. Apply focused applications of specific nutrients (such as boron or nitrogen) to correct nutrient deficiencies, as needed, while avoiding additions of nutrients that are at relatively high levels. For example, nitrogen is extremely mobile in soils, while phosphorus tends to build up over time. Adding focused applications of synthetic (15-0-0) or organic nitrogen (in the form of feather meal) can help meet crop needs without providing excessive amounts of phosphorus, over time. Gardeners who annually apply organic matter to their soils, without the benefit of a soil test, may be unintentionally adding too much phosphorus to their soils. Soils with excessive micronutrients may hinder plant growth. Soils with excessive phosphorus might contribute to water quality issues in their watershed. Excessive phosphorus also harms or kill beneficial mycorrhizal fungi.

Master Gardener Input Needed!

We are soliciting Master Gardener feedback on the attractiveness of the native wildflowers that Aaron Anderson is studying for pollinator plantings. More detail on the study can be found at:

http://blogs.oregonstate.edu/gardenecologylab/native-plants-2/

As we mention, not only are we interested in finding plants that support ecosystem services; we also want to find plants that gardeners find attractive, and that they would want.

This is where you come in. If you are willing, please let us know which ones you would like to see in your own garden, based on their looks, alone. Below is the recruitment letter, with further information about participation. Thank you for your consideration!

*******************************************

Study: Screening Willamette Valley Wildflowers for attractiveness to Pollinators and Natural Enemies

Graduate Research Assistant: Aaron Anderson (andeaaro@oregonstate.edu; 503-860-9286)

Principal Investigator: Dr. Gail Langellotto (Gail.Langellotto@oregonstate.edu; 541-737-5175)

Dear Master Gardener,

You are invited to take part in a survey that will generate useful information on the ornamental value of pollinator-friendly native wildflowers.

Previous research has shown that urban greenspaces, notably gardens, can provide excellent habitat for pollinators and other invertebrates. The inclusion of pollinator-friendly plantings in gardens has the potential to improve habitat quality and connectivity in otherwise inhospitable landscapes. However, research on which Willamette Valley wildflowers are best to use for these plantings is lacking. Thus, I am conducting a research project to assess the relative attractiveness of 23 wildflower species native to the Willamette Valley (Oregon) to pollinators and natural enemies. Additionally, I would like to assess the aesthetic value of these plants to identify native flowers that are also attractive for ornamental use in home gardens.

As a Master Gardener, I am asking your help with my study, “Screening Willamette Valley Wildflowers for attractiveness to Pollinators and Natural Enemies”.  If you are aged 18 or older, and are currently a Master Gardener, or have been a Master Gardener in the past, I would appreciate it if you could take 10-15 minutes to respond to this survey:

http://bit.ly/OSUNative

Your survey responses will be recorded as a group. Thus, your response will be anonymous.  If the results of this survey are published, your identity will not be made public. The security and confidentiality of information collected from cannot be guaranteed.  Confidentiality will be kept to the extent permitted by the technology being used.  Information collected online can be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses.

Your participation in this study is voluntary and you may refuse to answer any questions(s) for any reason.  There are a limited number of Master Gardeners in Oregon, so your participation in this study is important. If you do not want to participate and do not wish to be contacted further, do not fill out the online questionnaire. There are no foreseeable risks to you as a participant in this project; nor are there any direct benefits. However, your participation is extremely valued.

If you have any questions about the survey, please contact me at 503-860-9286 or via email at andeaaro@oregonstate.edu.  If you have questions about your rights as a participant in this research project, please contact the Oregon State University Institutional Review Board (IRB) Human Protections Administrator at (541) 737-4933 or by email at IRB@oregonstate.edu.

Thank you for your help. I appreciate your consideration.

Sincerely,

Aaron Anderson