As populations of bees and butterflies decline in the Midwest, native prairie restoration becomes crucial. A new Prairie Research Institute study found, however, that many commercial seed mixes used to conserve and restore prairies may not have enough diversity or spring flowering plants to fully support these pollinators.

“Imagine being an insect and waking up in the spring. You’re metabolically stressed and you go to a habitat made just for you, but there’s no food available for two months,” said Jack Zinnen, a PRI wetland plant ecologist and lead author on the study. “That’s why a lack of plant diversity is a big deal.”

The study compared 196 seed mixes designed for pollinators against 102 prairie remnants in eight states, finding that the seed mixes offered less blooming richness and fewer early-blooming species.

“The irony is that you have these seed mixes that are explicitly for pollinator conservation, but they will not be supporting pollinators well for the first part of the growing season,” he said.

The paper, published in the journal Restoration Ecology, builds on Zinnen’s previous research that included a survey of 557 plant vendors selling native plants across the Midwest and investigated the contents of commercial seed mixes. The new study compared the diversity of wildflowers in pollinator-specific seed mixes to that of prairie remnants, which are prairies that remain undisturbed by agriculture or development.

Zinnen found that most mixes contained few, if any, plant species that bloom before the second or third week of June. About 28% percent of wildflower species in the remnants studied flower by the end of May, compared with 0-13% in seed mixes.

Most mixes also contained fewer than 25 different plant species, at best half the diversity of prairie remnants. Remnants contained 50 to 100 different wildflower species on average, with as many as 150 wildflower species in some of the most diverse examples. Most of the seed mixes were made up of a handful of grasses, with the majority of blooming plants peaking in late July to early August. 

Pollinator restoration is becoming more popular, and the industry is growing. Zinnen said encouraging the use of mixes with 40 to 50 different plant species, rather than just 25, would be ambitious but would offer better support for pollinators and create a more resilient habitat.

Another recommendation would be for mixes to include species that become established easily, bloom in the spring, and tend to be hardy. Some examples Zinnen suggested were wild strawberry, wild garlic, golden alexander, spiderwort, and wild indigo.

The economics of species selection is also a consideration. Grasses are less expensive than other types of plants and are used to fill up the space in conservation areas. Some wildflowers are more expensive than grasses but are popular because of their beauty. They also contribute to a greater diversity. 

In another recently published study, Zinnen and colleagues found that some native plants — like orchids, pondweed, sedges, and ferns — are harder to find for sale, meaning they’re underrepresented in the commercial market. The native plants that are more widely available tend to live longer, grow across larger areas, do well in slightly disturbed habitats, and are often shrubs or trees. The availability of plants and seed mixes from commercial vendors is significant, the authors write, because it “can influence the composition and outcomes of conservation, landscaping, and restoration plantings.”

The greatest demand for seed mixes in the Midwest comes from private landowners in the U.S. Department of Agriculture’s Conservation Reserve Program and state agencies planting natural areas and roadsides.

The Prairie Research Institute at the University of Illinois Urbana-Champaign provides scientific expertise and transformative research to the people of Illinois and beyond. PRI is home to the five state scientific surveys: the Illinois Natural History Survey, Illinois State Archaeological Survey, Illinois State Geological Survey, Illinois State Water Survey, and Illinois Sustainable Technology Center.

Media contact: Jack Zinnen, jzinnen2@illinois.edu, 217-891-3235