Illinois Department of Transportation’s Seeding Standards and Best Management Practices

Abstract

To provide evidence-based revisions to Section 250 of the Illinois Department of Transportation roadside specifications manual, we conducted a literature review, an experimental planting, and a survey of previously planted roadsides. We created newly designed native seed mixes and field tested these mixes in comparison with existing IDOT mixes. After one year of growth in lawn, roadside, and slope areas, we found overall positive effects on native species cover using the newly designed native mixes. We surveyed 34 native species plantings along roadsides in Indiana and Illinois and evaluated several variables to determine which factors led to long-term establishment, finding cover by seeded native species and native species overall increased with distance from road and decreased with increasing soil nitrate and phosphorous. We further found that number of native species and seeded native species increased with distance from road and greater seed mix diversity, whereas richness of non-native, non-seeded species was greater at shorter distances from the road. Across all sites, 84 of the 150 native species seeded at sites were never observed in our surveys, but 28 native species were observed at more than half of the sites in which they were seeded. Our results suggest native plantings can persist on roadsides for several years after planting, but that specific site-level factors increase the likelihood of long-term success.IDOT-R27-25