The germination process requires the accumulation of heat units known as growing degree days. In general the accumulation of approximately 100 to 125 GDD are required for corn seedlings to emerge. If soil is cold at the time of planting, additional GDDs may be required to warm the soil around the seed to approximately 50 degrees F, sufficient to facilitate germination. Corn needs a minimum temperature of approximately 50 degrees F, soil moisture, and light for germination.
While a minimum temperature of approximately 50 degrees F is required for germination, it is not advisable to base planting decisions on soil temperature alone. Soil temperature in the seed germination zone fluctuates considerably based on ambient air temperature and, therefore, is not a dependable indicator of when to plant.
Modern corn hybrids appear to maintain viability for long periods from planting to emergence. However, increases in the time of emergence generally result in increased variability in time of emergence between plants. This loss of symmetry in emergence can compromise grain yield.
Damage from cold temperature stress adversely affects the germination of seeds and the growth of young seedlings and probably predisposes the plants to invasion by soil fungi capable of causing seed rot and seedling blight. In addition to slowing the germination process, cold temperatures, especially if accompanied by precipitation (snow and freezing rain), may cause irreparable harm to the delicate structures of emerging corn seedlings. When dry corn seed absorbs cold water as a result of a cold rain or melting snow, “imbibitional chilling injury” may result. Cold water can cause similar injury to seedling structures as they emerge during germination. Such injury in corn seed ruptures cell membranes and results in aborted radicles, proliferation of seminal roots, and delayed seedling growth. When temperatures remain at or below 50 degrees F after planting, damage to germinating seed can be particularly severe. When this physiological damage is combined with surface soil crusting, saturated soil conditions, compacted soils, deep seed placement, and seedling blights, you have a recipe for widespread emergence problems.
For more information on this or other topics related to corn production, contact your state extension corn specialist or your local extension educator/agent.
Following is the link to the corn extension specialists: state extension corn specialist.