It’s mid-April and corn planting season is almost upon us. True, for some farmers there is already some corn in the ground. But for those who are barely started or who don’t have any corn planted yet because of wet, cool weather this spring, don’t be intimidated by the calendar.  

That’s the advice of Mark Licht, Iowa State University Extension cropping systems agronomist. Planting is one of the most important, if not the most important, field operation of the year. And now is a good time to think about planting considerations. Often Licht is asked what planting date is best for corn in Iowa. In order to answer that question, he says he first needs to know what the growing season will be.

Trying to predict growing-season weather this far ahead is probably not going to be very accurate. “So, we have to rely on past results, comparing different planting dates over the years, to give us the best indications of when corn planting should occur,” he says.

Choosing a specific date is risky
Generally, the corn planting window in Iowa that results in achieving 95% yield potential is from April 15 to May 5. For soybeans, the optimum planting window shifts to April 25 to May 15. That’s what ISU research over the years has shown. Picking a specific planting date is pretty risky, notes Licht.

Deciding when to start planting should not be determined by date alone, but rather by a combination of date and local field conditions, he advises. Wait to plant until soil temperature is 50 degrees F and rising. That temperature measurement should be taken at the 4-inch depth. Also, you should wait until soil moisture is adequately dry to minimize the risk of sidewall compaction.

Keep in mind that soybeans like slightly warmer soil conditions than corn for germination and emergence. And no matter whether you are planting corn or soybeans, pay attention to the weather forecast.

Watch 5- to 10-day weather forecast
The importance of the five- to 10-day weather forecast is to ensure that germination and emergence occurs in a timely manner, says Licht. When it comes down to it, cold injury to corn (imbibitional chilling) occurs when cold, wet conditions occur within 24 to 48 hours of planting. Don’t push planting the last 40 acres just to get those acres in before a cold rain. Doing that will hurt your stand establishment and diminish seedling vigor.

It’s best to plant corn when the soil is warm enough to germinate the seed, but not so early that the young plants are likely to be damaged by frost. Agronomists agree that you shouldn't plant corn until soil temperature is 50 degrees at the 4-inch depth. Iowa State University provides the three day forecast and soil temperatures by county. Click here for the latest weekly USDA National Ag Statistics Service (NASS) crop condition report for Iowa. 

“Planting early can give the corn plants time to mature before they face the stress of Iowa's summer heat and can lead to increased yields at harvest,” sums up Licht. “As ISU research shows, the optimum dates for planting corn range from mid-April to the end of April in north- central and northeast Iowa, with the first or second week in May being ideal for other parts of the state.” 

Follow planting action on social media
According to USDA’s recently issued Prospective Plantings survey, Iowa farmers intend to plant 13.3 million acres of corn in 2017. That’s down 4% from 2016. Iowa soybean acres are projected to climb to 10.1 million acres, a 6% increase over a year ago. Nationally, growers are projected to plant a record 89.5 million acres to soybeans this year, right behind corn’s nearly 90 million acres.