Planting Date Trends

Encyclopedia Article

The fact that corn is now planted earlier than ever before is not a surprise to most producers or agronomists in Iowa. Using data provided by USDA-NASS (National Agricultural Statistics Service) for Iowa, we can clearly see that substantial changes have occurred over the past three decades. One way to compare across the different periods of time is to look at the date associated with 50% of the acreage planted. For Iowa, the trend to earlier planting is consistent as the 50% dates are earlier for each period compared to the previous except for two (1985-1989 and 2005-2009); see Figure 1.

Diagram of the percentage of corn planted over a range of dates, graphed by year.

Figure 1. Iowa corn planting progress, 1975-2009. 

Since 1990, producers have begun planting at approximately the same time (15 April). Producers are starting earlier and finishing sooner, yet the total time required for planting has changed little over time as most producers take six to eight weeks to finish. Changes in land size managed per individual producer are one of the primary reasons for this length of time not changing. When looking at the data set as a whole, planting dates are earlier although wet springs will cause fluctuations in the observed trends. For example, the period of 2005-2009 included several years with late springs and therefore, the average response is slower than the period of 2000-2004.

Numerous factors enable producers to plant their acreage earlier. Wider planters coupled with more cold-stress tolerant hybrids, improved seed treatments, and reduced tillage systems have each contributed to this change. As producers farm more acreage, they must naturally start earlier if they want the majority of their corn planted during the optimum planting window for their region. This is based on the fact that producers face a larger yield reduction by planting too late rather than too early.

Iowa State University Agronomy Extension Corn Production