Frequently Asked Questions
How does planting prairie plants in roadsides help bees and butterflies? Aren't they just killed by vehicles anyway?
Native prairie roadside grasses and wildflowers provide important sources of food and shelter for bees and butterflies. Studies suggest that in roadsides with less frequent mowing and more types of prairie plants butterflies are less likely to cross the road and be killed, possibly because they don't have to cross the road to search for more habitat. Research also suggests the relative proportion of the local pollinator population killed by vehicles is relatively small and there is a net benefit to having habitat available in the roadside. Collisions may increase during fall migration for monarch butterflies and in areas with high traffic counts. For more information, see the Xerces Society's website on pollinators and roadsides and Monarch Joint Venture's frequently asked questions about monarchs and roadsides.
Will native plants in the roadside attract deer and increase deer-vehicle collisions?
Because deer prefer to forage on young, green grasses, which occurs after mowing, reduced mowing can reduce the attractiveness of roadside vegetation to deer. However, studies in Florida and North Dakota have found no effect of reduced mowing on deer-vehicle or wildlife-vehicle collisions. The factors affecting deer-vehicle collisions are complex, but in Midwestern areas with a lot of agriculture, variations in traffic volume and the abundance of deer may be better predictors of deer-vehicle collisions than landscape composition, although there also appear to be a lot of deer near wooded areas. For safety, native plants aren't planted too close to the road edge, intersections, or driveways to preserve sight lines so drivers can see the edge of the road well.
Do prairie plants plug tile lines?
Video footage taken by Iowa State and the Tallgrass Prairie Center of different farms has shown few if any prairie roots infiltrating tile lines and certainly not obstructing tile lines. Tiles in low-lying areas may become plugged by reed canarygrass, an aggressive non-native plant that is never included in prairie seed mixes.
Will native plants spread from the roadside into adjacent farmland?
Iowa State's STRIPS team has planted strips of prairie directly within cropland for farmers who are interested in soil conservation, improved water quality, and habitat. The researchers have found that prairie plants do not spread well into tilled or conventionally sprayed farmland.
Aren't tall prairie plants in the roadside a safety risk?
As noted in responses to other questions on this page, safety is always first. Tall prairie vegetation is not planted in the clear zone, or the area of the roadside closest to the pavement, to improve drivers' ability to see. Because deer are attracted to browsing on freshly mown vegetation, reduced mowing may reduce the attractiveness of roadside vegetation to deer although so far studies have shown no relationship between reduced mowing and deer-vehicle collisions. Reduced mowing is a safety benefit to road department personnel who spend less time mowing steep slopes, providing fewer opportunities for accidents or items in the roadside being hit and thrown from the mower into traffic.
Studies indicate that drivers are drowsier when roadside scenery is monotonous and that roadsides with many different types of plants may increase driver alertness, possibly reducing crash rates, although there are no studies specifically looking at the effects of native prairie vegetation on driver alertness. The seed mixes provided by the Iowa Roadside Management program contain 20-38 plant species, adding variety to the species seen in the roadside. The tall prairie vegetation may also provide a softer landing for vehicles that go off the road, slowing down a vehicle more than short grass.
Mowing is needed to keep the vegetation short in some areas of the roadside, such as the part closest to the road pavement, intersections, and driveways so drivers have good sightlines. However, in other areas of the roadside further from the road frequent mowing for safety purposes is less necessary. Over the last 15 years, more state DOTs have been cutting back on mowing to save money and establish pollinator habitat; counties and cities can also experience savings from reduced mowing. Replacing one acre of cool-season grasses such as Kentucky bluegrass, fescue, or smooth brome with prairie will be more expensive than just mowing these grasses the year that the prairie is planted. However, once the prairie plants establish they do not need to be mowed as often as cool-season grasses, which saves money on fuel, equipment, and labor.
This handout uses information from the City of Cedar Falls mowing research to demonstrate cost savings by replacing one acre of turf with prairie over five years. Although the handout is not specific to roadsides and the exact costs may vary by county or city, it captures the resources needed to establish prairie and how cost savings through reduced mowing can be realized over time. Unlike the example in the handout, while counties and cities with an IRVM plan need to provide the labor, mulch, and equipment to plant prairie in the roadside, they can receive roadside prairie seed for free (a value of $220-$375/acre through a large seed purchase from the Tallgrass Prairie Center) and apply for grants from the Living Roadway Trust Fund to partially cover the costs of the equipment.
Since it takes prairie plants three years to mature won't a lot of erosion on steep roadside slopes occur in the meantime?
Roadside managers typically include a fast-growing cover crop such as rye, oats, or winter wheat when planting prairie plants in the roadside. Rye, oats, and wheat cover the ground and reduce erosion while the slower-growing prairie plants are establishing. The prairie seed mixes include some species that establish more quickly than other prairie plants, like Canada wildrye and black-eyed susan. Many roadsides are hydroseeded with a mulch that also contributes to providing erosion control.
How do prairie plants in the roadside improve water quality?
With their dense roots, prairie plants act like a sponge to effectively filter and remove pollutants. The dense roots also mean prairie plants are more effective competitors against weeds than cool-season grasses such as fescue and smooth brome; fewer weeds means less herbicides need to be used for weed control. For more information about prairie roots, click here.
How do prairie plants in the roadside help reduce erosion?
Warm-season grasses that are included in prairie seed mixes for roadsides include big bluestem, Indiangrass, and switchgrass; these grasses and some wildflowers have dense roots that are up to 6-9 feet deep. These dense roots make them especially suitable for reducing soil erosion, in comparison to shallow-rooted cool-season grasses such as tall fescue, with roots up to 2-3 feet deep. Many engineers and roadside managers have found prairie plants reduce erosion and site erosion control well. Research on prairie strips planted within farmland has found prairie grasses to be effective in reducing erosion.
Some people think seed mixes with warm-season grasses are too complicated to plant and take too long to establish. However, a stand of native grasses and wildflowers can be established successfully without increased erosion if: proper seeding depth is used when planting, weeds are effectively controlled with herbicides and mowing during the first year to reduce weed competition, and quickly-establishing cover or nurse crops such as oats are planted with the seed mix.
How does having a roadside manager help a county or city be more efficient and manage for safe, healthy roadsides?
A roadside manager provides leadership and efficient use of government resources by:
- being the one-stop shop, the go-to person who is familiar with a county or city's roadside vegetation; using their knowledge, they proactively prioritize smart ways to manage weeds and brush, mow, and plant and manage native plantings that are cost-effective and reduce environmental impacts
- saving money with strategic mowing and herbicide use
- saving money by applying for free native prairie seed from the Tallgrass Prairie Center and grants from the Living Roadway Trust Fund to help cover the costs of roadside management equipment and roadside vegetation inventories
- serving as a resource for residents who have questions about their own conservation and land management projects, for example knowing where to buy supplies such as erosion control products
- being available to manage weeds and prairie plantings during windows of opportunity when weather conditions are best; especially on a county's many small roadside projects, contractors might not have the flexibility to show up quickly when conditions are right for managing a given weed, producing better results that don't have to be fixed later on
- participating in two annual meetings and a Google group where the roadside manager community learns from each other and from experts about best management practices
Does my county have a roadside manager? How do I learn more about encouraging them to start a roadside program and hire a roadside manager?
Check this map to see if your county has a roadside manager. If the engineer is listed as the main roadside vegetation contact for your county, the county likely doesn't have a separate roadside manager on staff. Contact Kristine Nemec at the UNI Tallgrass Prairie Center (email@example.com, 319-273-2813) or Tara Van Waus at the Iowa DOT (firstname.lastname@example.org, 515-239-1768) to learn more about how other counties have started a program or resources we can provide.
If you have any other questions, please contact Roadside Program Manager Kristine Nemec at email@example.com or 319-273-2813. She can answer your question or direct you to the right person or resource. Resources for the information on this page are available on request.