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.
