2014-2017 Progress Report NRCS Plant Materials Center, Corvallis, OR June 2018 Evaluation of Commercial Pollinator Seed Mixes for Western Oregon: Third Year Progress Report Amy Bartow and Annie Young-Mathews ABSTRACT There are many pollinator seed mixes available on the commercial market, but not all are likely to establish and perform well in our region, or provide high quality pollinator habitat. The purpose of this study is to evaluate a number of commercially available pollinator mixes for use in western Oregon. Started in the fall of 2014 at the Corvallis Plant Materials Center (PMC), this study includes small plots of seven different commercial pollinator mixes seeded at a standardized rate of 60 seeds/ft2. Plots were monitored every two to four weeks throughout the 2015, 2016, and 2017 bloom seasons (late February through September) for plant canopy cover, bloom period, flower abundance, and pollinator visitation. After three years of evaluation, we have found that the most important trait in a mix, for providing continuous bloom over multiple years to attract the most pollinators, is the right balance between annuals, short-lived perennials, and long-lived perennials. Annuals provide first year bloom and cover while the perennials are becoming established, but usually fall out completely by the third year. Short-lived perennials bloom heavily in the second year, usually re-seed, and continue to fill in bare areas in the planting. Long-lived perennials will continue to bloom every year after the first establishment year and expand over time. INTRODUCTION Pollinator habitat requires an array of plants that flower throughout the entire growing season. This provides a source of nectar and pollen for adult pollinators and a diversity of herbaceous plants important for immature pollinator life stages and nesting (Pendergrass et al., 2008; USDA- NRCS, 2016). The commercial seed industry is marketing pre-made seed mixes appropriate to attract pollinators. These mixes may not perform equally in different regions of the country. Some commercial mixes may contain plant species that can become invasive, or the mix may not contain appropriate species to provide pollinator forage throughout the year, or may not contain plant species that provide forage to the target pollinators (i.e., not all flowers are of equal value to pollinators). Where commercial pollinator seed mixes are being marketed, the PMC may determine it beneficial to evaluate commercial mixes against a standardized pollinator mix to be able to advise NRCS field offices and their customers on the commercial mixes’ relative value in providing pollinator forage. The purpose of this study is to evaluate seed mixtures for pollinator habitat value in western Oregon. Amy Bartow, Seed and Plant Production Manager, USDA-NRCS Corvallis Plant Materials Center, 3415 NE Granger Ave, Corvallis OR 97330, [email protected] MATERIALS AND METHODS Treatments in this study included a “standard” Xerces Society pollinator seed mix and six other commercially available wildflower/pollinator seed mixes (Table 1). The standard was developed for western Oregon by Corvallis PMC staff and staff from The Xerces Society for Invertebrate Conservation in 2014; it was designed to provide a continuous bloom throughout the growing season (at least three flowering species in early, mid-, and late season), including species that are readily available and relatively low in cost. Other mixes were selected for inclusion in this study from commercially available wildflower or pollinator mixes for the Pacific Northwest that 1) did not include any invasive or noxious weeds, 2) would likely provide abundant bloom throughout the season, 3) included some late-season nectar and pollen sources, 4) had a balance of annuals and perennials, and 5) provided a variety of flower color, shapes and sizes to accommodate different pollinators. The species composition of each mix is listed in the individual mix descriptions in Appendix 2. Fall 2014 plots (Round 1) were seeded at the Corvallis PMC on a Woodburn silt loam soil that had previously been in native perennial grass production for over five years. A firm seedbed was prepared by plowing followed by harrowing and rolling with a smooth roller. Non-replicated 20 x 50-ft plots were hand broadcast seeded and raked in on 23 September 2014 and it rained heavily the following day. Seeding rates were standardized to apply 60 seeds/ft2, but the vendor- recommended seeding rates and associated costs are also given in Table 1. Plots were not fertilized or irrigated during this study. Soil tests in May 2015 showed that the field had a pH of 4.9, high levels of P and K (133 and 258 ppm, respectively), and medium levels of other nutrients (9 ppm SO4-S, 4.3 meq/100 g Ca, and 0.7 meq/100 g Mg). A second set of plots were seeded in fall 2015 (Round 2), also on a Woodburn silt loam soil that had previously been in largely unmanaged turf for at least five years. Seedbed preparation was similar to the first year, and 20 x 50-ft plots were hand broadcasted and raked in on 8 October 2015. Soil tests in July 2016 showed that the field had a pH of 4.9, high levels of P and K (58 and 265 ppm, respectively), and medium levels of other nutrients (3.5 meq/100 g Ca and 0.9 meq/100 g Mg). Table 1. Pollinator seed mixes included in the 2014-2017 trials at the Corvallis Plant Materials Center. Vendor PMC Trial Rate Recommended at 60 seeds/ft2 Seeding Seeding Rate Rate Cost No. Oregon (lb per Cost per (lb per per ¼ Vendor Mix Name Species Natives* Annuals* ¼ ac) ¼ ac ¼ ac) ac American Native Pacific 18 UNK UNK 5.5-11 $394-787 3.3 $233 Meadows Northwest Wildflower Nature’s Northwest Wildflower 17 0% 47% 5.5 $275 1.8 $91 Finest Seed Blend Silver Falls West Cascade 17 68% 46% 2.25-3 $162-216 2.3 $162 Seed Wildflower Economy Xerces Pollinator Mix 2014 23 82% 26% 3.5 $230 3.5 $230 Society Silver Falls Native Pollinator Mix 18 48% 58% 3.75 $218 3.8 $218 Seed Heritage Wetland Prairie 21 100% 24% 1.25-2 $163-260 3.8 $488 Seedlings Flowers 1 Heritage General Pollinator 20 100% 25% 1.75-2.5 $229-328 5.5 $721 Seedlings Mix *Western Oregon native and annual species compositions are based on seed weight percentages in each mix. UNK= unknown. 2 Weed control consisted of one hand weeding of all plots in May 2015 and May 2016, and mowing in late fall each year after all plants had senesced. Weather data for the study period were collected from the Oregon State University Hyslop weather station. In general, the 2014- 2015 season in Corvallis was warmer and drier than average, the 2015-2016 season was warmer and wetter than average, and the 2016-2017 season was cooler and much wetter than average. Total precipitation for the October through May growing season was 35 inches in 2014-2015, 47 inches in 2015-2016, and 57 inches in 2016-2017, compared to a 20-year average of 39 inches. During the bloom period (late February through September 2015, March through August 2016, and April through August 2017), all plots were evaluated monthly for pollinator visitation, and bi-weekly for bloom period and flower abundance. Bloom abundance was measured by counting the number of open flowers of each species in 10 random 1-ft2 quadrats per plot. Pollinator visitation was monitored using the Streamlined Bee Monitoring Protocol for Assessing Pollinator Habitat (Ward et al., 2014). This protocol consists of conducting timed 7.5-minute counts of all floral visitors along two sets of two 50-ft transects (total of 15 minutes along 200 ft per plot). Pollinator visits were recorded in the following broad categories: honey bees, bumble bees, other native bees, wasps, flies, and butterflies/moths. Where possible, we tried to document which insects were visiting which flowers. Photographs were also taken monthly at established points in each plot. Canopy cover data were collected monthly during the establishment year of each set of plots (2015 and 2016), and once per year in June thereafter. Canopy cover was recorded by species at 1-ft intervals along a 50-ft line-point intersect transect running diagonally across each plot; all canopy layers were recorded in order to capture small native seedlings that might initially be hiding under weedy cover. This study is a non-replicated demonstration, so no statistical comparisons are possible. RESULTS AND DISCUSSION Establishment and canopy cover In general, establishment rates for all mixes appeared to be much higher in the Round 2 plots (seeded in the fall of 2015) than in the Round 1 plots (seeded in the fall of 2014), with most mixes having at least 75% canopy cover of planted species by mid-summer in 2016, while weed cover and bare ground topped 50% in many mixes during mid-summer of 2015 (see cover charts for each mix in Appendix 2). Since site preparation and planting dates were similar in both years, this difference in establishment is difficult to explain, but may be due to a combination of varying pest pressure (slugs and birds), weather, and field history/weed pressure. Species composition and canopy cover changed dramatically from Year 1 to Year 2 in both rounds of plantings, as many annual species failed to reseed the second year, and the aggressive biennial riverbank lupine became dominant in most mixes where it was present. One exception to this loss in plant species diversity was the Xerces Pollinator Mix, which had an increase in the number of species present in the cover data in Year 2 as perennial species became the dominant cover.