Maurice - The seedling did not die right away. In fact, it appeared to go dormant and then produced some small leaves, but then those disappeared, too. I've no idea what happened. But the older leaves did turn somewhat yellow and drop unlike it's siblings. The small leaves just fell away from the plant. Perhaps root rot?
Something did occur to me though .... it bloomed for the first time this past Spring. I forget how many blooms. I think 6 or so. I pollinated all the blooms and got pods from each. That may have stressed the plant too much. I did not hybridize it's siblings as much but 1 or 2 blooms.
I'm learning. Before, it never occurred to me not to overdo the hybridizing efforts on young seedlings. I probably should have only hybridized 1 or 2 blooms last season instead of all of them. That takes too much energy away from such young seedlings.
It's a shame. I really loved the bloom on this seedling.
As far as soil temps, most of my daylilies are in raised beds. I wonder if I should probably invest in a shade cloth to place over those beds during the hottest part of the summer?