Mowing and Wildlife

Mowing for Monarch Butterflies

Monarchs typically have four generations each year, with the final generation migrating south to their overwintering habitat in Mexico. Breeding generations require milkweed to reproduce, and the migratory generation requires abundant nectar to fuel their migration. This essential habitat can be found in some roadsides.

Because adult monarchs feed on nectar from a variety of flowering plants, not just milkweed, leaving blooming plants preserves valuable food sources for adults. Delaying mowing until after July 15 leaves habitat for early generations of monarchs in Iowa. If possible, delay mowing until after Oct. 1 to help all breeding and migratory monarchs (Monarch Joint Venture).

What About the Deer

Because deer prefer to eat tender new plant growth over tougher older vegetation, reduced mowing may discourage deer from foraging in roadsies.  

A study conducted for the Federal Highway Administration found that deer-vehicle collision rates were not related to how often the Departments of Transportation in Maryland and New York mowed [Normandeau Associates, Inc. 2012]. Accordingly to research conducted by the Indiana DOT, mammal and bird road kill was not significantly different between roadsides with short vegetation and roadsides planted with tall shrubs [Road and Kirkpatrick 1985]. These studies suggest that letting roadside vegetation grow tall doesn't increase deer-vehicle collisions, although research is needed. s.

What You Can Do

  • Before July 15, only mow roadsides as needed for safety, spot weed control, and removing competition for native prairie seedlings.
  • Delay haying and mowing for brush control until after July 15.
  • Delay mowing until after July 15 to promote game bird and songbird nesting habitat and reduce soil erosion from spring rains.
  • To best help monarch butterflies, delay blanket mowing until after Oct. 1.
  • If you wish to harvest hay on state roadsides, contact the Iowa DOT maintenance garage or contact listed on the DOT website: IDOT
  • Along county roadsides, contact your county engineer or county roadside manager to learn more about Integrated Roadside Vegetation Management, which uses selective mowing and Iowa’s native plants in county roadsides. 

Mowing and Birds

Songbirds and game birds often nest in roadsides during May or June. If the first nesting attempt fails because of weather, predation or mowing, all upland game bird species and most songbird species will re-nest.

The first two weeks in July are critical in game bird reproduction because this is when young chicks from the second nest hatch. Delaying mowing until after July 15 allows 20 percent more nests to hatch versus a July  mowing (Iowa DNR). Leaving roadsides unmowed also provides a safe corridor for birds to move around the landscape.

Tallgrass Prairie Center

The Tallgrass Prairie Center is a strong advocate of progressive, ecological approaches utilizing native vegetation to provide environmental, economic, and aesthetic benefits for the public good. The Center is in the vanguard of roadside vegetation management, native Source Identified seed development, and prairie advocacy. The Center primarily serves the Upper Midwest Tallgrass Prairie Region and is a model for similar efforts nationally and internationally.