As spring approaches and farmers and agronomists get anxious for the growing season to begin, the same question arises each year. When is the best time to begin planting?

This question is often argued between farmers and agronomists, with farmers typically wanting to plant earlier and agronomists advising to wait. This argument is often followed by an “I told you so” by one or the other, depending on growing season conditions and harvest results.

In Indiana, the optimum planting window for maximum corn yield potential occurs between April 20 and May 10. For southern counties, this window may shift one week earlier, and for northern counties, it may shift one week later. Overall, when examining previous-year planting progress for Indiana from USDA National Agricultural Statistics Service crop reports, planting progress typically increases around April 20, with most planting finishing toward the end of May.

Previous research has shown that corn yield potential begins to decrease about 0.3% per day once planting is delayed beyond May 1, and about 1% per day if planting is delayed until the end of May. These decreases in corn yield potential are often contributed to a shortened growing season, elevated pest pressure, and increased potential for high heat and dry conditions during pollination.

However, it is important to understand that delayed planting may only impact potential yield and not actual yield in a specific year. Just because corn was planted late doesn’t mean high yields won’t be achieved. Many different factors and conditions beyond planting date can impact actual corn yield throughout the season. In certain instances, late-planted corn can outyield early-planted corn due to exposure to various conditions throughout the season.

Chasing a calendar date to get corn planted is often not the smartest decision. For example, chasing a calendar date can result in corn being planted in less-than-ideal soil conditions, causing issues such as soil compaction, poor root growth, uneven emergence and seedling disease, all of which ultimately result in lower yield.

Soil temperature debate

Soil temperature is also always a hot topic each year as planting approaches. Pictures of digital thermometers placed in the soil are often shared as everyone waits for the infamous 50 degrees F to be achieved to begin planting.

However, it is important to remember that corn typically needs 115 growing degree days to emerge. If the soil temperature is at 50 degrees and continues to average only 50 degrees for a length of time, corn can take upward of 35 days to emerge; whereas if corn is planted into a soil with a daily average temperature of 65 degrees, emergence can occur in seven days or less. The overall goal is to achieve rapid emergence of corn plants to shorten the period an emerging plant is exposed to certain stresses, limit the potential for uneven emergence and achieve more stress-tolerant plants.

The bottom line is that when corn planting season approaches, pay more attention to specific soil conditions and the upcoming weather forecast, rather than chasing a specific calendar date or a specific soil temperature of 50 degrees when making the decision to start planting.

Quinn is a Purdue Extension corn specialist.