For many producers, spring planting is late. While everyone is anxious to get a crop planted, corn yield may not be as tied to planting date as we think. In fact, planting into good soil conditions may be just as important as planting date.
 
We found that planting date has little effect on corn yield. We had 625 fields from Central Kentucky where we compared yield to planting date. The resulting curve had an r-square of 0.0823, which basically means that there is no relationship between planting date and yield in Central Kentucky (Fig. 1). When comparing planting date to yield from 59 fields in the Green River area, the r-square was only 0.1512. Again, there is very little relationship between planting date and corn yield.
 

For each year, the highest yield was set to 1 and all other yields were adjusted. Highest actual yield was 233 bu/A in 2011. The Central Kentucky fields had planting dates that ranged from April 2 to June 2 from 2003 to 2011.

Highest yields were reported for planting dates of The Green River Area fields were planted from April 10 to May 21 from 2010 to 2012. Having data from 2003 to 2011 spans a large range of environments and conditions. We would always welcome more data. The more data we have from more locations around the state, the better picture we can get on planting date and yield.

Historically optimal planting dates range from April 1 to May 1 in western Kentucky and April 15 to May 15 in central and eastern Kentucky. However, the ideal dates for a single year can vary widely as seen in Figure 3. For Central Kentucky, the best planting date in 2005 was April 10. In 2009, the best planting date was May 29. For 2011, the best planting date was May 31.

While planting date is important, it probably is less important than planting into good soil conditions and it is certainly much less important than July rainfall.