Planting date research has shown that the optimum corn planting period for much of Michigan is from the beginning to middle of May. Numerous studies have shown that there were no agronomic or economic advantages to planting corn before April 20.
Together with soil moisture, the soil temperature determines the ideal planting time for many Michigan crops. The minimum threshold temperature for corn seed germination is 50 degrees Fahrenheit in the seed zone. Corn will germinate unevenly when soil temperatures are less than 50 F.
Thermal time from planting to emergence is approximately 115 growing degree days (GDDs) using the modified growing degree formula based on air temperatures or about 119 GDDs based on soil temperatures. When soils warm to the mid-50s or warmer, emergence will occur in seven days or less if soil moisture is adequate.
Previous planting date research by Michigan State University Extension specialists has consistently shown there would be no agronomic or economic advantages for planting corn before April 20 in Michigan. For much of Michigan, the optimum corn planting period usually is from the beginning to middle of May.
Because of the shortness of this optimum planting period, most growers plant some corn before and after the optimum dates. If the field conditions are right and the calendar says late April, then plant corn if the soil temperature is above 50 F. If, however, the soil conditions are not right, then delay planting until early May without a yield penalty.
We have experienced several seasons where weather conditions got sunny in April and farmers planted corn only to find freezing conditions return several days later. This resulted in poor germination and the need for replanting.
Typically, soil takes a longer time to warm up than the air temperature. An inexpensive soil thermometer gauge is all you need to keep tabs on soil temperature 2 inches below the soil surface. You can also visit the MSU Enviro-Weather website to check the soil temperature and several other important weather features from a station closest to you.
Also, make sure your planting date is within the planting period specified in your crop insurance policy.