Seed Mixes

Take advantage of prairie diversity

Native roadside seed mixes need to include species adapted to a wide range of growing conditions, from wet to mesic to dry. To outcompete weeds, the mix should also include species that occupy different ecological niches within the planting, grass species and broadleaf species, warm-season and cool-season species, tall plants to shade out thistle seedlings, and small plants to fill in underneath.

When working in narrow ditches, such as those found within a 66-ft. right-of-way, it is most efficient to design one mix that includes species for a wide range of site conditions — from the gravelly, well drained soils at the top of the slope, to the heavy, saturated soils at ditch bottom. Apply the same mix over the entire area and let it sort itself out. Wider rights-of-way may have wet or dry areas large enough to justify designing and planting a seed mix specific to those spots.

To achieve a well-rounded mix with all the benefits native vegetation has to offer, include species from each of the following functional groups. The Tallgrass Prairie Center’s Designing Seed Mixes technical guide and seed calculator can also be helpful for designing seed mixes.

A well-rounded native seed mix will include species from each of these groups:

Quick-Establishing

Some native species develop faster than others. These are important for early erosion control and provide positive PR while slower species establish. 

Warm-Season Grasses

Roadside plantings rely heavily on these prominent members of the native plant community. These grasses continue to grow through the hot summer months. They provide long-term erosion control and good fall color.

Cool-Season Species

Plantings are strengthened by a species component that greens up early in the spring. These plants provide late-winter/early-spring erosion control and occupy the niche sought by non-native, cool-season competitors like smooth brome.

Legumes

The prairie flora includes many legumes that thrive in roadside plantings. They fix nitrogen and improve habitat.

Showy and Easy

These species establish readily, are relatively inexpensive and create masses of color noticeable at 65 mph. They are crowd pleasers. 

Showy

The following species cost a little more or are harder to establish but still add important color and habitat.

Early Bloomers

It’s relatively easy to extend a planting’s blooming season into the fall. Spring color is harder to come by. The following plants provide the earliest color visible from the road.

Wet Species

Upland species dominate roadside seeding mixes. Species adapted to wet areas are needed for moist ditch bottoms.

A Note About Tall Grasses and Non-Native Perennials

For visibility and safety, tall grasses — such as big bluestem and Indiangrass — should not be planted at intersections or driveways. Omitting these grasses throughout the remainder of a planting, however, will limit its adaptability. Big bluestem and Indiangrass are versatile, adapted to conditions from medium-dry to medium-wet. Short native grasses, on the other hand, are generally adapted only to dry sites.

Non-native perennials — such as tall fescue, perennial rye, crown vetch, and birdsfoot trefoil — are very competitive and will persist to the point of adversely affecting survival of native seedlings. These species should not be used in permanent or temporary mixes for sites planted to natives.

Seed Mixes for Shoulders

Native species are not used on the shoulder. Examples of seed mixes that withstand repeated mowing and are well-suited to shoulder conditions follow.

• 50% Kentucky, 31% fescue, and 50% perennial rye

• 45% Kentucky, 31% fescue, 45% perennial rye, 6% medium red clover, and 4% alsike clover

• 35% Fawn fescue, 35% perennial rye, 20% timothy, and 10% alfalfa, or hairy vetch

Roadside Manager Insights

Keep in mind in most situations we’re not recreating a diverse prairie. We’re stabilizing the roadside with native plants.

-Joe Kooiker, Story County, 2024

Aspect/shading sometimes need to be taken into account, especially on small plantings or problem areas. In shaded areas, we use savanna species in the mix. If there’s a lot of shade, we may plant a nonnative, cool-season mix. 

-Jim Uthe, James Devig, Dallas County, 2024

We use local ecotype hand-harvested forbs and combined seed from our native seed nurseries to add diversity to our roadside seed mixes. 

-Joe Kooiker, Story County, 2024

Try to tailor your mix so the ROW has color all year long.

-Joe Kooiker, Story County, 2024

Depending upon soil type, we may use up to a 1.5x the rate of native seed to help speed establishment and stabilization. 

-Jim Uthe, James Devig, Dallas County, 2024

Seeding Rates

Put down enough good seed to get timely vegetative cover and ensure planting success

Steeper slopes require heavier seeding rates. To get adequate erosion control, it’s more affordable to increase the amount of grass in the mix than to increase forbs. The result is that roadside plantings tend to have a higher grass to forb ratio than other prairie restorations. No matter how much native grass seed is put down, at least a 25% forb component is recommended to achieve adequate diversity and long-term stability. A 50% forb component is considered adequate for a fairly diverse planting. Some counties—especially those with their own forb seed plots—may exceed 50% for intersections and other highly visible plantings.

Grass to Forb Ratio

To get adequate erosion control, it's most affordable to increase the amount of grass in the mix. No matter how much native grass seed is put down, at least 25% forb component is recommended to achieve adequate diversity and long-term stability. 50% is better.

Seeding rates are calculated in one of two ways:

• Seeds per square foot 
• Lbs./acre

Though frequently used, lbs./acre is not a precise way of measuring the number of seeds planted since seed weights vary greatly between species. For example, one ounce of compass plant contains 660 seeds, while one ounce of black-eyed Susan contains 92,000 seeds. When accurate calculations are desired, use seeds/ft.

Seeding rates for roadside mixes are determined by slope and – to a lesser degree – seeding method. Budgets can also be a factor. The following chart provides general guidelines – a good idea of how many seeds should be put on the ground.

Minimum Recommended Seeding Rates

These rates apply to drill seeding, broadcast seeding and hydroseeding (two-pass method). When hydroseeding with seed mixed in the slurry (one-pass method), increase rates by 15–30% to compensate for seed hung up in the mulch. (Note: Under real working conditions, even the best attempts at measuring seed quantities in the field will not be perfectly precise.)

The Iowa Prairie Seed Calculator will help you if you would like to create custom mixes.