I'm growing Purple Passion asparagus from seed. Twelve sprouted in newspaper pots. I have them under flourescent lights for about 14 hours a day. I up-potted them to 3" peat pots a few weeks ago when roots started appearing out of the newspaper. Height varies from 3-5". Last week, one of the seedlings started turning yellow at the tips of their ferns, and is now completely withered and dead. Three more are now yellow at the tips of their ferns.

Any idea what could cause this?