Corn germinates best in soil temperatures greater than 50 F with a sharp decrease at temperatures below 50 F. Germination is slow in cool, dry soils and will speed up as soil moisture increases until the soil is at field capacity. Saturated soil conditions will prevent or retard germination because oxygen concentration, which is required for germination, is too low around the seed. Before germination, the seed imbibes water and swells. With warmer temperatures less water has to be absorbed, so that germination will start earlier and progress faster at higher temperatures. Emergence has been known to occur in as little as 4 to 5 days when soil temperature and moisture are optimum.
Deeper planting can delay emergence.
A general rule of thumb is one day delay for each one inch deeper depth. Since spring soil temperatures decrease with depth, emergence delays could be the result of both cooler temperatures and greater distance for the shoot to travel. Cold, wet weather has been the experienced by Wisconsin growers over the last couple of years. For example, some species of Pythium are active at these temperatures. However, seed rot and seedling blight will occur infrequently when using good quality seed and proper seed treatment.