Soil temperature in the seed zone should be 55°F or greater before planting. Corn seed will sprout slowly at 55°F while germination is prompt at 60°F. Delay planting if cold weather drops soil temperatures below 55°F at the two-inch level. However, if soil temperatures are 55°F and higher, and projections are for a warming trend, corn planting should proceed.
Early planted corn out-yields late planted corn. Usually, as long as the growing point is below ground level, corn can withstand a severe frost or freezing damage without yield reduction. It is best therefore to monitor soil conditions and weather if your desire is to plant as early as possible.
Use of GDDs
Many management decisions for corn depend on the growth stage and development. The growth stages are controlled by the amount of Growing Degree Days (GDD) the corn plant receives. GDDs are a useful tool to gauge the development of your corn and provides insight into whether stress is occurring. Under optimum conditions a corn plant will progress to a given stage in a certain amt of GDDs. When plant progression does not line up then we know that the corn plants were stressed in some way.
GDDs are easy to determine just check your local weather station (ours is Dixie, GA) and look for Degree Day Calculator. Enter the date of crop emergence and the current date.
Here are a few slides from Dewey Lee showing the effect of GDDs: