I have been trying to harden my seedlings outside. However, for the rest of this week, temps will go down to the low mid 40s every night. Can Daylilies Seedlings Withstand Low 40 Temps? Should I take them back inside? Can I just go ahead and plant them in this weather? It is going to be a cool wet and cloudy week.

I don't hybridize and I don't have a lot of seedlings. But I believe I am right in saying a lot of the large hybridizers plant all their seeds outside in the weather and let them grow. That way they get some idea of which ones are hardy and suitable for their climate. I know my little seedlings have been though freezes and frosts and now are getting pretty large. We are warmer down here, but I think even up north some of the breeders plant outdoors.

40 degrees should be ok as long as it doesn't drop into freezing temps.

Karen, the seedlings should be fine with temps in the 40's. If they have a good root system started, and you're able to plant perennials in your area now, you can go ahead and put them in the ground.
The seedlings I started back in Jan. were put outside in their trays a week ago. So far they have only seen one or two mornings above freezing, been frosted most nights and had 1 1/2 " of snow fall on them Tuesday. There may be a few that are struggling, but the large majority will handle the temps and weather without any problems. I would plant mine now if I didn't have so many other things to do in the garden. Once I get caught up a little in the next 2 weeks I will start planting 2 - 3 trays a day.

A cool wet cloudy week is just what I look for to plant my seedlings. We move ours outside in a shady area and then after a few days or a few weeks depending on what we have going on, they go from their shade tree trays to the garden. Any seedlings with decent root systems will most likely be fine. I would not be concerned if the temps got to 30F.

Thank you very much! I will try to plant them out this week. They look like they want to get out of their small cells.