Guide to planting cover crops in Minnesota

The earlier you plant, the more growth your cover crop will achieve in the fall.

• If you’re interested in a winter-killed crop like forage radish or oats, you’ll need to get it planted after a small grain or canning crop to get substantial growth.
  • Within a corn-soybean rotation, it’s probably safest to start with overwintering cover crops like cereal rye, triticale or barley. 
• If you have livestock, you may want to tailor your cover crop planting to maximize forage production or quality.
  • Cover crops can be hayed or grazed, with temporary fencing and water.
  • Make sure that any residual herbicides used in the cash crop are approved for grazing after the appropriate interval.

Do’s and don’ts

• Try to use a cover cop from a different plant family to minimize the risk of plant disease carryover, and maximize plant diversity, which is beneficial for soil microbial communities. 
• If you’re planning to plant wheat next spring, don’t use cereal rye as a cover crop. Instead, choose oats, so that any volunteers that come up in the wheat crop can be killed.
• If cover crops are planted after Aug. 15, use cool season crops, as there isn’t enough time for adequate growth to justify the costs of legumes and brassicas.
  • These may include forage pea, barley, wheat and triticale.
  • In Minnesota’s northern climate, there may not be enough time to truly benefit from a legume's nitrogen credit.
  • Average biomass and N produced by cover legume cover crops can be found at the Midwest Cover Crop Council’s Selector Tool.

Consider herbicides

• When planting cover crops, also consider herbicide carryover and rotation restrictions.
• Look at herbicide product labels or call your agronomist for exact restrictions.
• Remember, the label is the final authority.

Herbicide rotation restrictions in forage and cover cropping systems

A cover crop that overwinters will provide the best soil protection through the winter and into spring. However, you’ll generally need to terminate it before planting the cash crop in the spring.

• A combination of cereal rye, which will overwinter, and radish (which will winter kill) is an example of a mix where the rye provides added soil protection, while the radish residue decomposes quickly.
• For a quick-growing grain that doesn’t overwinter, seeding barley in the fall is a good option.
• While typically winter-killed, turnips can overwinter, as they did in parts of Minnesota and North Dakota in the 2015-2016 winter.
  • If radish is in the mix and there aren’t grazing cattle, then another cover crop that serves the same purpose as radish isn’t needed.

Seeding methods

There are several choices for seeding cover crops:

• A no-till drill.

• Slurry-seeded (keep manure agitated for a more even spreading of seed).

• Broadcast and lightly incorporated for seed-to-soil contact.

• By plane.

• Interseeded by drill or broadcast (requires high clearance equipment if done late in corn season).

If the soil is moist, all of these seeding methods are viable options. If the soil is dry, leaving the seeds on the soil surface will reduce germination and coverage during the fall. 

Seeding depth and rate

As with any crop, seeding depth and rate varies by species. Minnesota-specific recommendations can be found from the  MN NRCS’ Tech Note 33 or the Midwest Cover Crops Council’s Selector Tool.

• Oats are better equipped to be seeded a little deeper if soil moisture is a concern.
• Peas also need to be seeded deeper than most other cover crops. 
• Seeding rates will always be lowest for drilling compared to broadcasting seed, as the increased seed-to-soil contact increase germination success.
• In general, when broadcasting or flying on cover crops, smaller seeds are a better choice. These include radish, turnip, flax, dwarf essex rapeseed, cereal rye and barley.
• Larger-seeded crops, like peas, sunflower, etc., should not be broadcast or flown on.

Consult with your seed dealers and other sources to select the right mix and rates for specific field and crop rotation situations. If you are receiving cost-share for cover cropping, make sure you follow the program guidelines for seeding rate and method.