Roadside native species seeding practices of Midwestern US departments of transportation

To counteract environmental problems associated with road construction and maintenance, road agencies have developed vegetation management plans that incorporate native seeding. We reviewed the specifications manuals from the Departments of Transportation of eight US states to synthesize information on native plant species used, seed mixes, site preparation, seeding methods, and maintenance to provide recommendations for roadside vegetation management. Manuals varied among states in terms of the species composition and functional diversity of plants listed for use. Individual mixes included an average of 14 native species, although some had as few as 3, and many lacked functional diversity or early blooming forbs that would benefit pollinators. We identified several early-blooming, low-cost, conservative plant species that could be incorporated into seed mixes. Compared to other states, Minnesota listed more native species and seed mixes, and provided detailed specifications for seeding, establishment, and maintenance, aligning well with recommendations based on ecological restoration research.