Corn planting date: When is the best time?

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Your seed corn is piled on pallets in the machine shed; your soil is cold and wet, and it is April 25.  But the weather forecast gives little chance of getting into the field for another week.  Your herbicide applicator has yet to show up and you have to wait for him.

You are faunching at the bit because it is getting late and Dad always said to start planting in April. Your spouse is tired of your griping, and your blood pressure and stress are just about to get you admitted as a cardiac patient.  We have a tip for you: erase your concerns about the calendar and planting date.  There is nothing magic about planting corn in April.

Bob Nielsen calls planting date a “conundrum,” sort of like a riddle, a puzzle, an enigma, or a mystery.  Nielsen is a corn production specialist at Purdue University and suggests you take conventional wisdom with a grain of salt. 

In his analysis of planting dates, Nielsen says very little corn was planted anywhere by April 21, but that is of little concern because only a relatively small percentage of acreage is planted by that date. 

Rhetorically, he asks, “What are the consequences of a delayed start to planting? How important a predictor of statewide corn yield is planting date anyway?  Does late planting in and of itself guarantee lower than normal yields?  Good questions, but the effect of planting date on statewide average corn yield is not clear cut.”  “Really,” you say!

Nielsen says over the past 20 years there has not been a strong relationship between the planting date and the statewide yield in Indiana.  And you can extrapolate that analysis to your state as well. 

He says planting date is only one of many “yield influencing factors” and it represents only 22 percent to 24 percent of the yield variability.  Nielsen acknowledges that the potential for yield declines after May 1 by 0.3 percent per day in early May and by 1 percent per day in late May. 

But he quickly adds, “Yield potential goes down with delayed planting because of a number of factors, including a shorter growing season, greater insect & disease pressure, and higher risk of hot, dry conditions during pollination.”

What Nielsen would like you to do to ease your concern about the necessity of planting in April is take the other yield influencing factors and group them together in a way they would create the maximum possible yield for the year on the optimum planting date. 

He says that might be 220 bushels per acre; or it could be 150 bushels per acre.  A 10 day delay beyond the first of May would have an impact of 10 multiplied by 0.3 percent per day decrease in yield. Applied to the 220 bushel yield would be 213 bushels per acre.  Applied to the 150 bushel yield would be 146 bushels per acre.

It is quite possible that the 146 bushel yield could occur when corn was planted in a given year on May 10, and the 214 bushel per acre yield could occur when the corn was planted the following year, on May 15. 

In this case, a larger yield was generated at a later planting date. 

Nielsen says, “A delayed planting of corn in an otherwise high yielding year may still be higher yielding than a crop planted on the optimum planting date in an otherwise lower yielding year. Farmers know this to be true because some have had June-planted crops in recent years that ultimately yielded better than any crop they have ever had.............. because the remainder of the growing season following the delayed planting was exceptional.”

He says look at 2009 and 2012.  2012 corn was planted early and yielded much less than the 2009 corn which was planted late, all because of the yield influencing factors other than the planting date.


Since planting date is only one of several yield-influencing factors, the date for planting corn has a much more minor impact than believed by many corn growers. Planting corn after May 1 may lead to lower corn yields; however that is only 23 percent of the determinant. It is quite possible for later planted corn to out-yield earlier planted corn.

Source: FarmGate blog

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