For Planting Corn, Soil Temperature Of 50 Degrees Is Magic Number

How important is soil temperature for determining when to start planting corn?

Published on: Apr 15, 2013

Agronomists say you shouldn't plant corn until the soil temperature is 50 degrees F at the 4-inch depth. How important is that number when you look at the calendar and see it's the 15th of April?

Related: When to plant corn in central Midwest

"That's kind of a magic number, 50 degrees, for planting corn," observes Jim Fawcett, an Iowa State University Extension field agronomist in eastern Iowa. "That's when corn will germinate, with a soil temperature of 50 degrees or higher.

"The reason for not planting before that is the seed actually will take up water with soil temperatures cooler than 50 degrees. The seed will swell, but it doesn't germinate. That's not a good combination because the seed will tend to rot if it's just sitting there swelling in the soil but not germinating. The seed imbibes the water, takes it in, but doesn't germinate because it's too cold."

EARLY PLANTING TIPS: Soil temperature and field conditions outweigh calendar date when deciding when to start planting corn. It is generally recommended to plant when soil temperatures are at or above 50 degrees F and the near-term forecast shows a warming trend. Planting into cold, wet soils puts stress on corn seed emergence, as does planting just ahead of a cold spell, says ISU agronomist Jim Fawcett.
EARLY PLANTING TIPS: Soil temperature and field conditions outweigh calendar date when deciding when to start planting corn. It is generally recommended to plant when soil temperatures are at or above 50 degrees F and the near-term forecast shows a warming trend. Planting into cold, wet soils puts stress on corn seed emergence, as does planting just ahead of a cold spell, says ISU agronomist Jim Fawcett.

Fawcett adds, "Particularly in April, I would definitely be paying attention to soil temperature before I decide to plant corn."

As for timeline, the ideal corn planting window is April 20 to May 5 in Iowa. "A lot of farmers have big planters and enough help that they can get their corn acreage planted in 3 to 5 days. If you can do that, there's no sense in trying to push things along before soil conditions are right," Fawcett says.


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