Now that Spring has Sprung, is it Time to Plant Corn?

Amy Shober, Extension Nutrient Management and Environmental Quality Specialist, ashober@udel.edu; Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu; Phillip Sylvester, Kent County Extension Agent, phillip@udel.edu; Cory Whaley, Sussex County Extension Agent, whaley@udel.edu; and Richard Taylor, Retired Extension Agronomist

After what seems to have been a never-ending winter, temperatures this weekend are projected to reach the high 70s. Thankfully, the extended forecast suggests that those frigid temperatures may be behind us. With the warmer temperatures comes the itch to get your corn planted. Here are some considerations for deciding when to plant corn.

Corn germination begins once the soil temperature at a 2 to 3 inch depth reaches 50°F. Currently, maximum daily soil temperatures in Georgetown are nearing that 50°F mark, but soil temperatures are dipping into the mid-40s at night. Waiting for soil temperatures to warm just a bit more will be important to achieving the uniform stands needed to maximize yield. While we should be starting to see soil temperatures increase with the warmer air temperatures, it is important to note that other factors may affect soil temperature. Fields that receive tillage, conventional or conservation, will tend to warm faster than no-till fields. Residue can act as a mulching layer, limiting temperature variability later in the season, but also delaying the effects of warmer air temperatures. Checking soil moisture content is also a good predictor of soil temperature, as moister soils will take longer to warm up.

Waiting for soils temperatures to warm a bit will decrease the likelihood of delayed germination. If it takes more than two weeks for corn to emerge after planting, there is an increased risk of variability in the growth stage of seedlings. When seedlings differ by two or more leaf stages (a two fully emerged leaf plant versus a four fully emerged leaf plant), the smaller plants can act more like a weed to the corn crop than a contributor to the field’s yield potential. Plus, with poor or uneven stands, there will be a more open canopy which may allow for weed emergence and increased weed competition.

We suggest you hold off on planting until the soil temperature reaches 50°F to ensure rapid and even germination. Soil temperature should be taken with a soil thermometer in several areas of the field, especially those with variable soil types. Fields with better drainage, sandier soil texture, or high organic matter, as well as fields that were tilled or that will be tilled are better choices for earlier planting, as these fields are likely to warm the fastest. You can also encourage soil warming by using row cleaners or strip tillage to allow direct sunlight on the soil surface that can help warm the seed row. Deeper planting will expose seed to cooler temperatures compared to those planted at shallower depths; however, we do not recommend a planting depth of less than 1.5 inches.

The use of starter fertilizers (at a rate that will sustain the crop until sidedress) can also promote more rapid and even germination. We recommend using fertilizers with a lower salt index on sandy soils and avoiding placement of fertilizers in-furrow (pop-ups) to limit the potential for salt damage to the seed or young seeding. High salt concentrations can damage and/or dry out emerging roots, leading to uneven emergence, which can potentially reduce yields.

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