When is it Time to Start Planting Corn?

March is here, planting intentions are high and our fields may dry out soon, if rain holds off. So when should we start planting corn? Normally, we can start rolling whenever soils dry out.  Last year, for example, early March plantings were very productive. However, temperatures have been cold for several days, so what effect might temperatures have on corn planting?

Adequate soil temperature is very critical to successful corn germination, emergence and early growth. Soil temperature is the primary factor regulating germination rate, which can affect stand success and plant growth uniformity, both of which are paramount to high corn productivity. The calendar date recommendations for planting are based upon normal conditions, which can vary from year to year, depending upon temperature and other environmental conditions. Corn seed germination requires a minimal soil temperature of about 50 degrees F and germination rate increases substantially as temperature rises. Soil temperature is far more important that of the air, because the corn growing point in underground until the V6 growth stage, which is normally at least 3 weeks after emergence. Thus, the best guideline for determining earliest planting date is when morning soil temperature at a 2-inch soil depth is 55 degrees F and/or at least 50 degrees F at a 6-inch soil depth. These levels generally ensure plant emergence within two weeks.

Soil temperature determines seed germination rate and needs to be at least 50 deg F or preferably warmer for corn seed.

Mississippi growers who planted in early March last year generally had very productive results.  This was because temperatures last March were extremely warm, producing an extraordinary response. Corn maturity is dependent upon heat unit accumulation measured as growing Degree Days (GDD). Last year, GDD accumulation during March was more than four times the normal, leading to unusually early corn development.

Although early planting is a critical component of successful corn production, planting corn very early will not generally produce the highest yields.  This is not only due to stand issues, but extraordinarily early planting usually enhances maturity very little and is not generally favorable for optimal vegetative development, because corn growth rate is correlated to temperature, and heat unit accumulation (GDD 50) is historically very low during early March.