Hi Brian:
To me that means when the first two or three break the surface (the hair pin). That means the others are also sprouting and not far behind and tells me it's time to put them under lights. It is possible under a lighting setup to raise the surface temperature too high which can actually spoil the sprouting seeds. Some seed lots are more sensitive to temperature than others. Generally, I've found temperatures of 65' to 72' F work good for me. And, you'll find that in some seed lots sprouting time varies quite a bit from start to finish. I have one seed lot going now that just sprouted two more and they were planted on Mothers Day, May 13th. I don't keep mine inside under light for any longer than I have to. I already had several lots outside in dapled shade by the time this last lot was planted.
