WASECA, Minn. – The wet spring continues to drag on and planting progress remains slow, but this is nothing new to growers. The norm may be to start corn planting in late April and wrap up in early May, but that just hasn’t been the case the last few years and yet there is always a crop to harvest in the fall.

“The way the seasons have been lately, we have had pretty adequate rainfall through the summer, and we have not been short on heat units,” said Tom Hoverstad, scientist with the University of Minnesota Southern Research and Outreach Center, during a phone interview on May 10.

Last year, and even the year before that, the spring was cold and growers lost some of those early growing degree days, but with a hot summer and late frost, those missing units were recovered by the end of the season.

“Today, we gathered 83 growing degree units, so missing out on those is not a big deal because our season is about 2,400,” said Hoverstad. “In the grand scheme of things, the heat units we have missed is not that big a deal.”

According to the USDA Crop Condition and Progress report, for the week ending May 12, 21 percent of the corn crop has been planted. This is an increase from 6 percent the previous week, where farmers only had about three days in the field.

Last year, at this same time, 36 percent of the corn crop was planted, so corn is only about 3 days behind last year.

Hoverstad states that growers we still able to harvest a decent crop as the first frost came later in the season.

“In 2018, September 29 we froze, but we had had some 2,700 growing degree units by then, we had a lot of extra heat last summer,” he said. “The year before that, the frost was even later.”

There is no question that corn yield potential does start to drop off as the planting date get pushed later into May.

“All you really can look at it is the long-term history. “We try to get corn planted by about the 5th of May, kind of as the optimum, somewhere in that April 20 to May 5 window,” he said. “From there, we start losing yield, but if not, we don't drop off drastically right away.”

Predicted yield loss starts out at around a quarter to a half a bushel of corn per day after May 5. Once planting gets past the middle of May, that loss expectation is around a bushel per day, according to Hoverstad.

“After May 20, we lose like two bushels per acre per day,” he said. “That yield decline kind of steepens later in the month.”

Hoverstad recommends that anything planted before May 20 can remain the grower’s original plan. Full season hybrids, 107-day corn, will still perform if planted before May 20. Shorter season, 103-104-day corn, will be fine if planted before May 25.

“Once it gets past the 25th of May, they probably need to be looking at shortening up the maturity to a 95-100 day,” he said.