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Plan now for successful decisions on corn planting

ST. PAUL -- With field work just around the corner, now is the time to evaluate decisions related to corn planting. University of Minnesota research can help you make decisions such as when to plant, what soil conditions to consider and how deep to plant.

Studies at the University of Minnesota Southwest Research and Outreach Center in Lamberton show that, on average, grain yield is maximized with an April 28 planting date, but planting between April 21 and May 6 produce similar yields. In central and northern Minnesota, optimum planting dates are generally a few days later. When corn planting is delayed beyond mid-May, yield potential is reduced rapidly.

Timely planting also increases the amount of time for in-field grain drying prior to harvest, but the advantages of timely planting can be lost if planting occurs when soils are too wet.

Sidewall smearing can occur on heavy soils when double-disk openers on the planter cut through wet soil, resulting in compacted soil around the seed that is difficult for seedling roots to penetrate. Seed furrows can also open up after heavy soil dries following wet conditions at planting. In general, a field is fit for seedbed tillage if soil from the top 3 to 4 inches breaks apart when pressed between your fingers rather than forming a ribbon or ball.

Corn requires soil temperatures of 50 degrees or higher for germination. The amount of time from planting to emergence has been shown to be reduced from 24 to 13 days when average soil temperature increases from 51 to 54 degrees. Quicker emergence decreases the potential for stand establishment problems.

In very late April, most agronomists agree that growers should ignore soil temperature and plant corn as soon as soils are fit, since warmer temperatures are expected soon afterward.

Planting depths of 1.75 to 2 inches are optimal for corn in most situations. Planting depths shallower than 1.75 inches increase the risk of poor establishment of the nodal roots that develop between the seed and the soil surface, which increases the potential for root lodging.

Finally, keep an eye on planting speed, as speeds above 5.5 miles per hour can result in excessive fluctuation in planting depth and within-row seed placement.

Pay attention to details this spring, as mistakes with planting last the entire season.

A detailed version of this article is available on University of Minnesota Extension's Crop News page at

Jeff Coulter is a corn agronomist with University of Minnesota Extension.