Garden Ecology Lab News, January 2018

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It’s been a busy month in the Garden Ecology Lab.

  • Gail’s manuscript on bees in home and community gardens has been published in Acta Hort. Briefly, the results of this literature review are that: 213 species of bee have been collected from a garden habitat; gardens have fewer spring-flying and fewer ground-nesting bees, compared to non-garden sites; I suspect that over-mulching might be cutting out habitat for ground-nesting bees in gardens.
  • Aaron presented his first Extension talk to the Marion County Master Gardeners. This 90-minute talk was an overview of using native plants in home gardens.
  • The entire lab is getting ready to present their research results at the 2018 Urban Ecology Research Consortium annual conference, to be held in Portland on February 5th. A few highlights of our presentations, can be found below.

Gail’s Poster on Urban Bees: we sampled bees from 24 gardens in the Portland Metro area (co-authored with Isabella and Lucas)

  • Langellotto and Messer UERC 2018 Poster: click to see preliminary results
  • Most of the bees that we collected await identification. We did find a moderate relationship between lot size and bee abundance: larger yards hosted more bees. But, we also found evidence that suggests that intentional design can influence bee abundance: one of our smallest gardens (site 56 = 0.1 acre), located in the Portland urban core (surrounded by lots of urban development) had the second largest number of bees (42), of the 24 gardens sampled. This garden was focused, first and foremost, on gardening for pollinators. The plant list for this garden (photos, below) includes: borage, big-leaf maple, anise hyssop, globe thistle, California poppy, nodding onion, yarrow, fescue, goldenrod, Phacelia, Douglas aster, lupine, mallow, columbine, meadow foam, yellow-eyed grass, blue-eyed grass, coreopsis, snowberry, Oregon grape, trillium, mock orange, pearly-everlasting, serviceberry, coneflower, blue elderberry, currant, milkweed, dogwood, shore pine, crabapple, cinquefoil.

 

 

 

 

 

 

 

 

Mykl’s Poster on Urban Soils: we sampled soils from 33 vegetable beds across Corvallis and in Portland (co-authored with Gail)

  • All gardens were tended by OSU Extension Master Gardeners.
  • Gardens were over-enriched in several soil nutrients. For example, the recommended range for Phosphorus (ppm in soil) is 20-100 ppm. Garden soils averaged 227 ppm. The recommended range for Calcium is 1,000-2,000 ppm, but the mean value for sampled beds was 4,344 ppm.
  • Recommended ranges gleaned from OSU Extension Publication EC1478.
  • There was a tendency for soils in raised beds to be over-enriched, compared to vegetables grown on in-ground beds.
  • Data suggests that gardeners are annually adding additional soil amendments or compost, and that there has a build up of certain elements in the soil.

Aaron’s Talk on Native Plants: measured bee visitation to 23 species of native and 4 species of non-native garden plants (co-authored with Lucas)

  • Field plots established at the North Willamette Research and Extension Center
  • In the first year of establishment, of the 27 flowering plants that were the focus of this study, seven natives (lotus, milkweed, camas, strawberry, iris, sedum, blue-eyed grass) one non-native (Lavender) did not bloom, or else did not establish
  • Several natives attracted more bees than even the most attractive non-native (Nepeta cataria, or catmint). These include:
    • Gilia capitata: Globe Gilia
    • Madia elegans: Common Madia
    • Aster subspicatus: Douglas’ Aster
    • Solidago candensis: Goldenrod

Garden Bees, 2017

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All bees have been pinned, labelled, and data-based. Now we’re (and when I say ‘we’re’, I’m mostly referring to Lucas and Isabella) are going through the painstaking process of photographing all specimens: head on, from the top, and from each side. We’ll then start sorting them by morphotype (how they look), and working to identify them. Some of the bees are very common, and fairly easy to identify (like Anthidum manicatum, Bombus vosnesenskii, Apis meliifera). Others will take a bit more time and expertise to get to species.

You can take a look at the entire album, representing about 150 of the nearly 700 collected bees. We’ll be adding the rest of the bees, as we can.

We collect and pin the bees, because most are difficult to identify, without getting them under a microscope, and without the help of a museum-level bee specialist. For those bees that are easy to identify by site (such as the ones listed above), we only collect one per garden (so that we have a record of its presence). We don’t collect multiple specimens of the same species, if we can identify it in the field. And, we don’t collect obvious queens (larger, reproductive bees).

We collect using a combination of water pan traps and hand collection. For hand collection, we use a pooter (an insect aspirator) for the smaller bees and baby food jars for the larger bees.

Water pan traps. We buy plastic bowls from the dollar store, prime them, and paint them with UV paint that is optimized for the wavelengths that bees see.

Here, I’m holding an insect aspirator, otherwise known as a pooter. You can suck insects off of flower heads without damaging blossoms, by carefully placing the metal part of the pooter, over the bee. It is then sucked into a small plastic vial, which I’m holding in my right hand.

This is such an exciting part of the research for me. I find myself obsessing over the photos, trying to organize them in my mind, and to at least get them to genus. Grouping them by genus makes it easier for an expert to sort through and identify them. And, I’m so grateful for their assistance, that I want to make it as easy as possible for them!

We’ve collected bees from gardens near Forest Park, in Portland’s city center, and in outlying suburbs. We’ll analyze the data to see if there are any patterns associated with garden location (forest, city, suburbs), or to see if there are specific bees that are only found in forest gardens, for example.

Pollinator of the Week: California Tortoiseshell Butterfly

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This entry is from Isabella Messer, an undergraduate horticulture student at Oregon State University. It highlights a common Oregon pollinator.

 

Despite the misleading name, we have unfortunately not discovered a new cross species between California butterflies and tortoiseshell cats. Even though this butterfly has a larval stage instead of a kitten stage, the California Tortoiseshell Butterfly is still a beautiful representative of the Lepidoptera. 

A California Tortoiseshell flashes its bright upperwing. Photo by Doug Backlund

As you may be able to guess, the largest populations of the California Tortoiseshell (Nymphalis californica (Boisduval, 1852)) are located across California(1). While the majority may be in California, the California Tortoiseshell habitat range stretches south from British Columbia to Mexico and east from California to Wyoming(1). When the California Tortoiseshells experience a population explosion in the summer(1), some populations have been known to travel as far east as Vermont, New York and Pennsylvania(2). 

These lovely butterflies can be identified by their bright orange upperwing which features black spots and black border(1). Their underwings are mottled brown and gray and resemble dead leaves(2). When in larval(caterpillar) form, N. californica can be identified by its all-black appearance with the exception of a white line running down its back and the slight blue at the base of its black spines(2).

The cleverly disguised underwings of the California Tortoiseshell. Photo by Doug Blackbund

Unlike some of the other pollinators that we have discussed over the months, the California Tortoiseshell Butterfly is somewhat picky when it comes to choice of host plant for the immature and habitat mature butterflies. Adults will oviposit (lay eggs) only on various species of wild lilac (Ceanothus) where the immature butterflies will be hosted until they reach maturity(3). Adult N. californica are less specific about their habitats by the time the reach maturity. They can generally be found in mountainous regions in chaparral, woodland and brush areas(1). 

While these charming butterflies may not be extremely common in the Portland area due to its low elevation, if you take a trip up to Mount Hood this coming summer, it is more than likely you will run into one of these beauties.

Sources:

  1. Lotts, Kelly and Thomas Naberhaus, et al. “California Tortoiseshell”. Butterflies and Moths of North America. 2017. Butterflies and Moths of North America. http://www.butterfliesandmoths.org/
  2. Ross A. Layberry, Peter W. Hall, and J. Donald Lafontaine. “California Tortoiseshell”. Canadian Biodiversity Information Facility. 9 Jul. 2014. http://www.cbif.gc.ca/eng/species-bank/butterflies-of-canada/california-tortoiseshell/?id=1370403265564
  3. Art Shapiro. “Nymphalis californica”. Art Shapiro’s Butterfly Site. http://butterfly.ucdavis.edu/butterfly/Nymphalis/californica

Plant of the Week: California Poppy

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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.

A native been rolls around inside of a California poppy at the North Willamette Research and Extension Center.

Having moved to Oregon from Michigan this past spring, one of my first memories of the state was the explosion of bright orange and yellow flowers lining the interstate and covering the hills. These ubiquitous flowers were, of course, California poppies (Escscholzia californica). Native to a range covering southern Washington south to the Sonoran Desert, the plant has spread throughout most of North America and onto other continents thanks to human intervention (1). This should come to no surprise to those familiar with the plant, because it is easy to grow and thrives in average soil, as long as drainage is good and there is plenty of sun (3).

California poppies can be grown as perennials or annuals, depending on the severity of the winters (3). The grey-green, finely divided foliage erupts with brightly colored flowers in the spring, but can continue flowering across the growing season if conditions are favorable (1). Long, spindly seed pods appear quickly following pollination and, once dry, easily explode, spreading baby poppies up to six feet away from the parent plant (1). If you’re looking to add these beauties to your own garden, it is best to spread seeds on the surface of the soil in the fall to ensure that dormancy is broken (1). But gardener beware: once established, California poppies are around for the long haul (3).

These flowers have been grown or collected for hundreds of years by the societies that have encountered them (1). Indigenous North Americans first used the plants for a variety of medicinal purposes and the plant quickly rose to fame in Victorian gardens after it was collected by David Douglas for the Royal Botanical Society of England in 1836 (1, 3). Western medicine has also found use of the California poppy, isolating over 30 chemicals for uses ranging from anti-bacterial agents to the treatment of cancer (1). For horticultural purposes, the Royal Horticultural Society today recommends planting along borders, for cut flowers, to create a sense of informality as in a cottage garden, as well as for gravel and rock gardens (4).

The act of gardening is unique in that it strikes a balance between control of and surrender to the natural world. On the one hand, the plants we decide to grow on our little slices of paradise are an irrevocable extension of us and our own stories; however, these plants have their own stories to tell and they transform us into participants of these stories whether we are willing or not. I’ve never heard anyone say, for example, that they planted such-and-such prize-winning hosta to attract deer to their garden. Yet, when these majestic 150-pound creatures sneak silently into our yards for a midnight snack, it’s hard to argue they weren’t invited. The plants we choose act as our ambassadors to a biotic world just beyond our grasp, providing food and habitat for a full spectrum of wildlife. On a larger scale, the landscapes we cultivate can collectively affect everything from water resources to the climate.

While it’s true that I’ve never heard anyone say they are planting for the deer, us gardeners have certainly taken a liking to another sort of creature. The insects of the Anthophila clade, otherwise known as the bees, have found a special place in our hearts. Maybe writer Michael Pollan was on to something when he recognized, in The Botany of Desire, the mirrored way in which the bees visiting his garden had found themselves in the servitude of the plants just as he was. While the gardener tends to the plants’ every need, the bee unwittingly ensures their reproductive success by transporting pollen from flower to flower. Or maybe its the recognition that we ultimately depend on pollinators for our own food security and survival. Whatever the underlying cause behind our species’ admiration of bees, cultivating a diversity of flowers is the surest way to invite them to and help them persist in our landscapes.

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

Whether you sow the seeds of the California poppy simply for its beauty, for its natural history, to help prevent erosion, or for any other reason, you will also inevitably be providing a source of food for our favorite insects, the bees. Surprisingly California poppies don’t provide nectar for pollinators, just pollen, but they are still heavily visited by our native bumblebees, sweat bees, and mining bees, as well as the European honey bee (Apis mellifera) (1, 2). They are also visited by beautiful butterflies, beneficial minute pirate bugs, and glistening beetles (1). Additionally, from our observations at the North Willamette Research and Extension Center, I can personally attest to the California poppy’s popularity amongst a variety of syrphid flies.

As a student interested in creating functional habitat for both humans and wildlife, it truly matters little to me on its face if a plant is native or not. Gardens consisting of native plants can be just as gorgeous and moving as gardens consisting of exotic species — this is true. What does matter to me are the relationships these plants have with other organisms, and what that looks like in a world increasingly and unavoidably modified by humans. So, whether or not you decide to bring the California poppy or any other native plants into your own garden, I hope you do feel inspired to think about these plants in terms of their role in the wider community of life with which we share this planet.

Sources:

  1. Smith, C. 2010. Plant guide for California poppy (Eschscholzia californica). USDA-Natural Resources Conservation Service, Plant Materials Center. Lockeford, CA 95237.
  2. Garvey, Kathy Keatley. “Why Honey Bees Forage in California Poppies.” Bug Squad: Happenings in the Insect World, University of California, 18 Mar. 2014, ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13179.
  3. Nelson, Julie. “California poppy (Eschscholzia californica).” Plant of the Week, USDA Forest Service Rangeland Management & Vegetation Ecology – Botany Program, www.fs.fed.us/wildflowers/plant-of-the-week/eschscholzia_californica.shtml.
  4. “Eschscholzia californica.” Royal Horticultural Society, www.rhs.org.uk/Plants/106119/Eschscholzia-californica/Details.

Pollinator of the Week: Virescent Green Metallic Bee

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A female virescent green metallic bee. Image from United States Geological Survey Bee Inventory and Monitoring Lab.

This entry is from Lucas Costner, an undergraduate horticulture student at Oregon State University. It highlights a common Oregon pollinator.

While there are approximately 4,000 species of native bees in the United States (an estimated 500 of which call Oregon home), I’ve decidedly landed on one as my very favorite (1, 2). This flying iridescent blue-green gem, covered in golden hairs, and sporting a pitch black abdomen with white or yellow bands is Agapostemon virescens, the virescent green metallic bee. Found throughout the United States and southern Canada, these members of the sweat bee family (Halictidae) are common and beautiful (3).

As with other species of the genus Agapostemon, the virescent green metallic bee is a communal soil nester (3). These nests are composed of underground tunnel systems, marked by a main vertical burrow that branches off into several larger nesting areas complete with horizontally running tunnels and cells (4). In these cells, female bees leave a gift of pollen and nectar for a single egg before filling the tunnel with an insulating layer of soil (4). Soon a babe is hatched and, after eating and growing, the mature offspring dig their way out to start foraging!

Virescent green metallic bees are polylectic, meaning they collect pollen from a wide variety of floral resources (4). This is lucky for us gardeners, because we can plant from over a dozen common flower genera and provide the bees with forage. This point is underscored by a 2014 study that sampled bee species in Chicago, finding that the virescent green metallic bee was one of the most common species in the city (5). The same study noted that in more densely populated neighborhoods, the overall composition of bees shifted to more heavily consist of  bees like the virescent green metallic bee and the European honey bee (5). As our cities continue to grow and the needs of urban communities become more pressing, this is good news for the virescent green metallic bee and other generalist pollinator species that can benefit from a relatively wide selection of floral resources.

A virescent green metallic bee emerging from a nest. Image from the University of Maine Cooperative Extension.

Having met the virescent green metallic bee for the first time this past summer working with Aaron Anderson on his native plants study at the North Willamette Research and Extension Center, I was curious to see which plants selected for the study had been previously identified as providing forage for the bee. From our list, the common sunflower (Helianthus annuus), yarrow (Achillea millefolium), showy milkweed (Asclepias speciosa), Douglas aster, (Symphyotrichum subspicatus), common camas (Camassia leichtlinii), wild strawberry (Fragraria vesca), Oregon iris (Iris tenax), sedum (Sedum oregonense), and goldenrod (Solidago canadensis) all make the cut (3).

Flowers are important for these bees for more than just food, however; as they also provide a rather scenic backdrop for the crucial business of mating. While female bees will return to the nest after emerging from the incubator cells in the spring, the male bees spend their days foraging, mating, and sleeping out in the cold, eventually dying at the end of the season (4). The females are the real beneficiaries of the underground nests, returning here to hibernate and lay their own eggs, and sharing in the joint responsibilities of guarding and maintaining the tunnels (4).

My favorite green bee may be relatively abundant and may not require as much help as other species in the way of specific planting regimes, but (as with all native ground nesting bees) leaving some undisturbed open space in your yard or garden can go along way to provide habitat. According to the Xerxes Society, nearly 70% of all native bees are ground nesters (6). To offer nesting habitat in your garden, simply leaving a couple feet of well-drained, bare or sparsely vegetated soil available in a sunny location will do (1, 6). The bees will take care of the rest — hopefully you will have the opportunity to enjoy them in your own garden next summer!

Sources:

  1. Moisset, Beatriz, and Stephen Buchmann. “Bee Basics: An Introduction to Our Native Bees.” USDA Forest Service, Mar. 2011.
  2. “Oregon Native Bee Atlas.” Oregon Bee Project, blogs.oregonstate.edu/beeproject/bee-atlas/.
  3. “Agapostemon virescens.” Discover Life, 9 Nov. 2017, www.discoverlife.org/mp/20q?search=Agapostemon%2Bvirescens.
  4. Abrams, Judith, and George C. Eickwort. “Nest switching and guarding by the communal sweat beeAgapostemon virescens (Hymenoptera, Halictidae).” Insectes Sociaux, vol. 28, no. 2, 1981, pp. 105–116., doi:10.1007/bf02223699.
  5. Lowenstein, David M., et al. “Humans, bees, and pollination services in the city: the case of Chicago, IL (USA).” Biodiversity and Conservation, vol. 23, no. 11, Oct. 2014, pp. 2857–2874., doi:10.1007/s10531-014-0752-0.
  6. Shepherd, Matthew. “Nests for Native Bees.” The Xerxes Society for Invertebrate Conservation, 2012.

Pollinator of the Week: Western Tiger Swallowtail

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This entry is from Lucas Costner, an undergraduate horticulture student at Oregon State University. It highlights a common Oregon pollinator.

A common feature of the urban and suburban landscape, a street lined with large London plane trees (Platanus x acerifolia), complete with lumpy trunks and exfoliating bark, can be a delight to behold. The tree was the favorite species of New York City planner Robert Moses, and became one popular choice for replacing elms affected by the infamous Dutch elm disease during the previous century (1). Chosen for its long life span, interesting growth habit, and ability to withstand the challenges of street life, the London plane has become a ubiquitous member of our cultivated environment. By happy accident, the tree also plays host to the larvae of the familiar and striking western tiger swallowtail (Papilio rutulus) (3).

This large yellow and black butterfly is found throughout the western continental United States and into southern British Columbia. Swallowtails tend to be specialists (2), so the addition of known host trees like the London plane and other members of the Platanus genus, along with willows (Salix spp.), poplars (Populus spp.), and alders (Alnus spp.) is of benefit not only to our parks, streets, and yards, but to these incredible pollinators as well (3). Adult females lay single eggs on the undersides of the leaves of host trees, which then provide food for the developing larvae (4). These larvae eventually form chrysalids and overwinter, emerging the following season as, well, beautiful butterflies (4). While the larvae of the western tiger swallowtail have somewhat specific tastes, the adult butterflies will feast on nectar from many flowering species. These pollinators typically take flight from June through July, but in Pacific coastal areas may be found throughout much of the year (3). They are noted as preferring wetter areas generally, and even as being avid visitors to mud-puddles (5).

Butterflies are of course important to us as gardeners because of the pollination services they provide, but throughout their lifespan they also play an important role as food for other organisms. Douglas Tallamy, from the University of Delaware, writes “if we were forced to care for only one group of insects in our restored suburban ecosystem, we would do well to choose the Lepidoptera” (the order consisting of moths and butterflies) (2). Fortunately for the western tiger swallowtail, and for those of us who enjoy its beauty, our cultivated landscapes should provide ample habitat. With that being said, global declines in flying insects are being documented (see: Insects are In Serious Trouble), and our attention needs to remain fixed as much on what we are planting as on how we are managing these landscapes.

Personally, I wasn’t fortunate enough to see many species of Lepidoptera this past season. I did manage to catch sight of a western tiger swallowtail early in the year, however, at the North Willamette Research and Extension Center foraging on a patch of showy milkweed (pictured above) neighboring the native plants study plot. Being a recent transplant from east of the Rockies, this was my first time ever seeing the butterfly and I was truly blown away. I’m hopeful that despite the challenges faced by these and other pollinators, we will all be able to enjoy them well into the future.

Sources:

  1. Jonnes, Jill. Urban Forests: A Natural History of Trees in the American Cityscape. Penguin, 2017.
  2. Tallamy, Douglas W. Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens. Timber Press, 2007.
  3. Haggard, Peter, and Judy Haggard. Insects of the Pacific Northwest. Timber Press, 2006.
  4. “Western Tiger Swallowtail.” Butterflies and Moths of North America, 21 June 2016, www.butterfliesandmoths.org/species/Papilio-rutulus.
  5. Layberry, Ross, et al. “Western Tiger Swallowtail.” Butterflies of Canada, Canadian Biodiversity Information Facility, 9 July 2014, www.cbif.gc.ca/eng/species-bank/butterflies-of-canada/western-tiger-swallowtail/?id=1370403265809.

Plant of the Week: Douglas Aster

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Image source: https://www.flickr.com/photos/12567713@N00/2809146063

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.

A common and much-beloved Northwest native, the Douglas aster, happens to be a bit of a misnomer. This profusely blooming, purple-flowered perennial isn’t a member of the Old World Aster genus, but rather belongs to the New World Symphyotrichum (2). As such, our Douglas aster (Symphyotrichum subspicatum) is closely related to its East Coast look-alike, the New England aster (Symphyotrichum novae-angliae), and evidence suggests the two descend from a common ancestor (2).

Naming conventions aside, the Douglas aster should be noted for offering an impressive, season-long (July – September) display of attractive, disk-shaped, and papery flowers while asking for little in return. Like many of the other native plants I have written about to this date, this plant is incredibly hardy and will spread via creeping rhizomes if given the opportunity (3). The USDA Natural Resources Conservation Service recognizes the Douglas aster as being abundant and present from Alaska to California, and into Idaho and Montana (1). In the wild, it is noted as being found in forests, along the banks of streams, and even along the coast (3).

In Oregon gardens, west of the Cascades, the Douglas aster will again require little in terms of care once established. It does prefer full-sun, and well-drained soil, but it similarly thrives in wetland areas (4). Our test subjects in the field faced many hardships, ranging from drought to over-zealous mowing, and still ended up thriving. Therefore, as with the majority of the native plants written about here, this plant may not be appropriate for every garden or indeed for every gardener. The most exciting part about the Douglas aster, however, is not its robust growth habit; but rather, its potential to benefit wildlife and therefore our suburban and urban environments.

In the field, other members of the Asteraceae family (think goldenrod and pearly everlasting) have anecdotally been some of the most popular plants in terms of pollinating visitors, and our Douglas aster plots were no exception. At times, it was hard to keep track of just which insects had or had not been counted during our five minute observations due to their sheer abundance. Thanks to the long bloom period, it was also exciting to the see the progression of pollinators develop as the season passed week by week, and the species composition gradually changed. While the Douglas aster is noted for its attractiveness to many species of butterflies, our observations could suggest that is similarly attractive to a fairly wide array of bees as well (4).

Sources:

  1. “Plant Profile for Symphyotrichum subspicatum subspicatum (Douglas aster).” Plants Database, USDA NRCS, plants.usda.gov/core/profile?symbol=SYSUS.
  2. Candeias, Matt. “How North America Lost Its Asters.” In Defense of Plants, 12 Oct. 2016, www.indefenseofplants.com/blog/2016/10/12/how-north-america-lost-its-asters.
  3. Knoke, Don, and David Giblin. “Symphyotrichum subspicatum.” WTU Herbarium Image Collection, Burke Museum of Natural History and Culture, biology.burke.washington.edu/herbarium/imagecollection.php?Genus=Symphyotrichum&Species=subspicatum.
  4. “Douglas Aster.” Washington Native Plant Society: Starflower Image Herbarium, 5 Nov. 2007, www.wnps.org/landscaping/herbarium/pages/aster-subspicatus.html.

Research Update: Studying Willamette Valley’s Native Plants

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Getting ready to install plants at our field site.

The post below comes from Aaron Anderson, a M.S. student in the OSU Department of Horticulture, and a member of the Garden Ecology Lab.

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This past summer, we conducted the first field season of a study screening native plants for their attractiveness to pollinators and natural enemies. We selected 23 native Willamette Valley wildflower species based on drought tolerance, as well as four exotic garden species known to be attractive to bees: Nepeta cataria ‘Catnip’; Salvia elegans ‘Pineapple Sage’; Origanum vulgare ‘Italian’; Lavandula intermedia ‘Grosso’.

Table 1.  Native plants selected for this study.

Plant Species Common Name Life History Bloom Color
Clarkia amoena Farewell-to-spring Annual Pink
Collinsia grandiflora Giant blue eyed Mary Annual Blue
Gilia capitata Globe gilia Annual Blue
Lupinus polycarpus Miniature lupine Annual Purple/Blue
Madia elegans Common madia Annual Yellow
Nemophila menziesii Baby blue eyes Annual Blue/White
Eschscholzia californica California Poppy Annual Orange
Helianthus annuus Common sunflower Annual Yellow
Phacelia heterophylla Varied-leaf phacelia Annual White
Acmispon (Lotus) parviflorus Annual White/Pink
Achillea millefolium Yarrow Perennial White
Anaphalis margaritacea Pearly everlasting Perennial White
Asclepias speciosa Showy milkweed Perennial Pink/White
Aquilegia formosa Western red columbine Perennial Red
Aster subspicatus Douglas’ aster Perennial Purple
Camassia leichtlinii Common camas Perennial Purple/White
Eriophyllum lanatum Oregon sunshine Perennial Yellow
Fragaria vesca Wild strawberry Perennial White
Iris tenax Oregon iris Perennial Purple
Sedum oregonense Cream Stonecrop Perennial Yellow
Sidalcea virgata Rose Checkermallow Perennial Pink
Sisyrinchium idahoense Blue-eyed grass Perennial Blue/Purple
Solidago canadensis Goldenrod Perennial Yellow

We planted them in meter squared plots at OSU’s North Willamette Research Center. Between April and October, we monitored floral visitation, sampled visiting insects using an “insect vacuum”, and tracked floral bloom.

With one season in the books, we have some purely anecdotal impressions of which wildflower species are the most attractive to bees. Goldenrod (Solidago canadensis) and Douglas aster (Symphyotrichum subspicatum) were both highly attractive to a wide diversity of native bees, as well as to a variety of beetles, bugs, and syrphid flies. As an added bonus, both these species had long bloom durations, providing habitat and colorful displays for significant portions of the summer. Annual flowers Clarkia amoena and Gilia capitata attracted a range of native bees; Clarkia was also visited by leafcutter bees for a different purpose – cutting circular petal slices to build nest cells with.

Bumblebee on Clarkia.

Syrphid fly on Goldenrod.

Results from this year need to be analyzed, and further research is needed to account for seasonal variability and to gather more data on floral visitors.

Additionally, w e will ask the public to rate the attractiveness of each of our study flower species in an effort to determine the best candidates for garden use. After a few more field seasons (and sorting lots of frozen insect samples!), the result of this study will be a pollinator planting list for home gardeners, as well as a pollinator and natural enemy friendly plant list for agricultural areas. These will help inform deliberate plantings that increase the habitat value of planted areas.

Studying Urban Garden Soils

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A soil pit is used to understand the nature of subsoil strata.

The Benton County Master Gardener demonstration garden was one of our soil test sites. This site had vegetables growing in raised beds, and in in-ground beds.

The Benton County Master Gardener demonstration garden used intercropping techniques to suppress weed growth in their beds.

This post is modified from a submission from Michael Nelson. It details lessons learned from his survey of garden soils, across Corvallis, Oregon, and the Portland Metropolitan area.  In September 2017, Michael sampled soils from about 25 gardens. These gardens used raised beds and/or in ground gardens to grow a variety of vegetables, herbs, and fruits. We wanted to study urban garden soils ~ and soils in raised beds versus in ground beds ~ for a few reasons. Specifically, we wanted to look at a few different questions:

  1. Do raised bed gardens offer greater protection from soil contaminants than in-ground gardens? In the Master Gardener Program, we recommend raised beds as a way to work around soils that may have heavy metal contaminants. However, heavy metals can become airborne, and deposited on soils from industrial emissions, traffic, and re-suspension of road dust. If this is the case, then gardening in raised beds might offer a false sense of comfort. We thus chose to sample gardens that are close to, versus further from, major roadways and traffic.
  2. Are garden soils deficient in some nutrients (such as nitrogen), but over-enriched in others (such as phosphorus)? With enthusiasm surrounding organic gardening and composting, we are wondering if repeated applications of compost might be contributing to nitrogen deficiencies, phosphorus leaching, or other soil nutrient issues.
  3. What is the general state of urban garden soils in Oregon? If we had to ‘grade’ soil health, by looking at soil structure, tilth, nutrients, and other biological, chemical, and physical characteristics of soils ~ what would that grade look like?

I asked Michael to write up a short report on his summer work. What did he observe in the gardens? What did he hear from gardeners? Are there initial findings or impressions he could share?  His report is below.

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We began this project to examine differences between raised and in-ground garden beds in urban areas. We conducted a short survey of each site, where we noted weed pressure, garden area (in meters squared), and crops grown. We also noted any concerns voiced by the gardeners, about their vegetable production site. We sampled garden beds and kept samples separate depending on the type of bed (in ground versus raised-bed). We are now processing the soil samples in the Central Analytical Laboratory of OSU, so that we can determine the chemical, physical, and biological characteristics of our garden soil samples.

A few initial observations:

  • The most common complaint we heard from gardeners was a lack of space to properly rotate their crops. For example, nearly every site had tomatoes, but many did not have the space to avoid planting in the same ground as the previous season.
  • In the lab, our initial findings are that garden soils do not fit well with traditional soil testing methods. The very high content of organic matter and low incidence of rocks brings immediate problems to the lab testing process. The first step taken when a lab receives a soil sample is to pass the sample media through a sieve. The larger pieces are lightly ground and sieved again. The aim is to isolate the soil from non-soil matter in order to restrict laboratory tests to just the soil content itself. The organic matter is often shredded by this process, which can alter the results of the laboratory tests. The primary problem here is that the organic material in our sampled garden soils is mostly forest by-products: timber waste. This material is generally inert in the garden setting and not accessible to plants. When this organic matter is included in a soils analysis, the organic matter compounds are incorporated into the test results and  skew the report away from the actual state of the garden’s soil.

The next steps in understanding garden soils are in research and application. In research, soil testing should be reconsidered with gardens in mind. There may be alternative processing techniques to reduce variability between test results and garden soil content. Theoretical models may be able to produce a metric which could be used to adjust the results of a standard soil test to reflect garden conditions more accurately.

In application, greater precision of terminology would allow for a more refined view and management of garden systems. In particular, bed-types should be grouped by their method of establishment (i.e. was soil transported to the garden, or not), rather than the presence or lack of a garden border. Additionally, organic mulches and compost should be considered in finer detail. The source of the product is important to determine what chemical content is being applied to the soil top. The physical structure of the product is important to relay the extent to which the mulch content will likely be incorporated into the soil, itself.

We’re still actively working to process and test samples. We look forward to sharing more results, in the near future.