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Finding the Right Pollinator Mix

A native bumble bee feeds on riverbank lupine (Lupinus rivularis) in a pollinator planting at the Corvallis, Oregon Plant Materials Center in May 2016.Do you get tired of preparing a custom seed mix for every person who comes into the office wanting to plant a pollinator garden? Have you looked longingly at the pre-blended wildflower mixes at the garden store or on Amazon.com and thought, “wouldn’t that work for me?” You’re not alone. Field office staff and other partners have asked that same question of their local Plant Materials Centers many times, and the answer is a resounding, “It’s complicated.”

Commercially produced wildflower seed mixes are readily available and broadly used for attracting pollinators and adding beauty to small gardens and landscapes. These mixtures are popular with landowners because they are pre-mixed and eliminate the guess work of designing custom mixtures. They also eliminate the need to search for and purchase individual species from multiple vendors to create a seed mix.

Most commercial seed mixtures are created to cover a wide range of adaptation and may include plants adapted to extremely low precipitation areas like arid deserts as well as plants adapted to wetter environments of montane forests. This range provides some insurance that at least some of the species in the mixture are adapted to a specific site and may thrive. However, a significant number of the species in the mixture are inevitably less likely to be adapted to the planting site and thus represent an unnecessary expense that can be avoided with some prior planning.

The species in the mixtures are selected for their attractiveness to bees, butterflies, and other pollinators and are purportedly well adapted to specific regions or environments. Despite these advantages, suitability of many of the species in the mixes to pollinator plantings for CRP or other NRCS programs is largely unknown. Many species are from North America outside of the target region; still others are of Eurasian or African origin. Additionally, 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. The mix may also contain plant species that are attractive to humans but provide little value to the pollinators.  Establishment, persistence, and suitability of many of these species to pollinator plantings are poorly understood in this context, and these issues need to be examined before NRCS can recommend commercially designed seed mixes for conservation practices.

Plant Materials Centers in Idaho, Oregon, and California installed comparative trials of multiple commercially available wildflower mixes to learn how the various species behaved and to determine the suitability of the mixes to NRCS programs. The PMCs evaluated various traits such as initial establishment, plant frequency or cover, weed presence, flowering times, bee visitation, and long-term persistence of over 100 species. 

In the Idaho study, approximately two-thirds of the original species (39 of 62) flowered in the first two growing seasons indicating at least moderate adaptation to the study area. Those that did not establish or flower add to the cost of the seed mix and may be included at the exclusion of more appropriate species. Careful selection of adapted species can reduce the cost of seed mixes as maladapted species are avoided. After 4 to 5 years, the plantings had narrowed down to a few dominant species. These species established well in our planting and were able to spread and flourish under the growing conditions at Aberdeen and are now being recommended for use in pollinator plantings in our service area. 

In the Corvallis, Oregon study, they 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 provided first year bloom and cover while the perennials were becoming established, but usually fell out completely by the third year. Short-lived perennials bloom heavily in the second year, while long-lived perennials will bloom every year after they establish and expand over time.

In the Lockeford, California study, most of the annual mixes evaluated for almond orchard floor use had good bloom from February to May the first year and all except the mustard mix reseeded the second year. The more diverse (and expensive) mixes of annuals and perennials intended for longer-term pollinator habitat in California’s Central Valley attracted more native bees than most of the annual mixes, particularly in the second year of the study as the perennials became established.

A native bumble bee feeds on riverbank lupine (Lupinus rivularis) in a pollinator planting at the Corvallis, Oregon Plant Materials Center in May 2016.NRCS funds or provides cost-share on approved pollinator plantings which meet agency specifications. These specifications include seed mixture composition percentages and the rate at which the seed is planted (lb/ac or seeds/ft2). 

To accurately calculate seeding rates, one needs to know: 

  • % of each species in the mix by weight, 
  • purity of each species, 
  • germination or viability of each species, and 
  • the average number of seeds per pound for each species.

This information is frequently lacking in commercial seed mixtures. Of the mixtures evaluated in Idaho, only two included percentage information, while 6 out of 7 mixes evaluated in Oregon provided percentage information. Species component percentages must be available to determine whether seeding mixtures meet NRCS standards. Mixtures not providing percentages of species components should not be used for NRCS-funded seedings.

Ultimately, the answer to the question, “can I use commercially available wildflower mixes?” is, “yes, you can, if those mixes meet NRCS requirements and goals of the planting.” You can ask for assistance from your local PMC to look at a proposed mix, or it may be possible for them to develop a small number of custom recipes for your service area, which you can provide to local seed vendors. For example, Derek Tilley of the Aberdeen PMC has developed a mix that can be used for general pollinator habitat at many sites in Idaho, Nevada, and Utah. Similarly, the ORPMC staff have developed recommendations for species that should make up the backbone of pollinator mixes for the Pacific Northwest. Your PMC staff and PM specialists are eager to help you put together the most beneficial and cost-effective mix for your site.