Corn planted April 13 in Michigan germination progress.

4/23 Update below: 2012's very early spring across the Midwest has prompted many farmers to put crops in the ground earlier than they ever have before. For us, we put this corn in on April 13th here in Michigan. Following a nice .6" warm rain following planting, by April 16 it had germinated, with soil temps holding in the low 60's at seed depth, despite a cold morning today with air temp of about 40.
4/23 update: We have experienced significantly below normal temps the last week, with frost several mornings. Soil temps at seed depth have dropped to 47 to 52. The Radicle root has continued to lengthen, and the coleoptile/plumule has emerged and is growing, still 1-3/4" below the surface. Development seems uniform across the field, so I am still hopeful of a fairly uniform emergence and stand. I suspect that having full germination (from the 4/14 warm rain) prior to this cold snap has helped a great deal. We also have remained fairly dry, and cold/dry is much better in terms of pathogens than cold/wet. We are a little warmer the next couple days, but are forecast to have one more shot at frost/freeze 4/26 and 4/27. This corn won't be emerged yet, and with most forecasts calling for a significant warming trend to average or above for the first week of May, this planting still looks decent, at least for now.