May and June are ideal seeding months, but road construction projects are rarely ready for seeding at this time. The following seeding calendar provides suggestions for protecting slopes and improving seeding success throughout the year.

January to mid-March

Winter months occasionally present windows of opportunity for frost seeding, a practice that originated as a way of incorporating seed into the soil when a native grass drill was not available. Seed is spread over bare soil made friable (loose or porous) by a cycle of freezing and thawing. Results can be good, but opportunities can be brief.

  • Be ready to jump on it. 
  • Include oats as a cool-season nurse crop.
  • Do not frost seed on areas covered with ice or snow.
    • Occasionally native seed is sown on top of snow. Technically this is not frost seeding, but can be an effective seeding method on relatively level sites.
  • Frost seeding on slopes is not recommended.

Late March through April

If site conditions permit (ground not frozen or too sloppy) this can be a good time for seeding. Warm-season grasses won’t germinate until soil temperatures reach 60 degrees Fahrenheit. Include oats as a cool-season nurse crop.

May and June

This time of year provides the best soil temperature and moisture conditions for germination and survival of warm-season species, including most prairie grasses and wildflowers.

July and August

Although every county can point to successful plantings during these months, hot, dry summer conditions are generally less favorable for planting natives. Consider a temporary seeding at this time, with the permanent, native seeding in the fall or the following spring.

If natives must be seeded now:

  • Drill, rather than hydroseed, for maximum seed to soil contact.
  • Increase seeding rate 25%.
  • Include appropriate nurse crop.
  • Mulch with straw, and crimp or tack straw into place.

September and October

Native seed germinating this late in the season is unlikely to develop enough root reserves to overwinter. Yet some of these plantings do succeed, maybe because a lot of the seed does not germinate until spring. Research is needed.

  • Erodible sites must be stabilized with winter wheat.
  • Increase seeding rate 25%.

November and December

Dormant seeding, considered a good option on level ground, is more complicated on erodible slopes. Cover crops seeded this late won’t provide erosion control until spring. The majority of native seed will remain dormant over winter. While some forb species do better when dormant seeded, some of the native grass seed planted at this time will deteriorate over winter.  

  • Erodible sites must be stabilized with winter wheat.
  • Increase seeding rate 25%.

Roadside Manager Insights

Timing is everything, watch the weather and don’t just seed a site to get it off the list.

-Joe Kooiker, Story County, 2024

Ideally, we begin dormant seeding in October or November once the 4” soil temperature reaches 50 degrees, but if erosion is a concern or there is an issue regarding a regulatory permit, we will seed earlier and may increase the seed rate some and hope for dormant seed.

-Jim Uthe, James Devig, Dallas County, 2024

I try not to seed in August, September, or early October. I prefer to wait until November, then drill into a cover crop and mow the following spring. If weather conditions deteriorate in November, I can still seed in the spring. However, there are many factors that can influence when seeding gets done including size of project, time available, topography, etc. Small sites and those that are not conducive to drilling typically get seeded as soon as possible.

-Wes Gibbs, Jones County, 2024

I don’t intentionally wait to frost seed. I might consider it, but only on flat areas in perfect conditions. 

-Wes Gibbs, Jones County, 2024