I'm trying them from seed for the first time this year, Littlebin. Do you keep yours potted?

Lizin, yes, mine is potted.
It is suggested to sink the pot in the soil in winter and put mulch on top if the winter is too cold.

I really doubt that ludlowii would have been winter killed unless you got super cold temperatures. It got to -9F, and none of my ludlowiis got any damage. Even the seeds managed to sprout, and they keep putting on leaves throughout the year.

This is my smallest one, but none of them took any damage despite being brand new plants last year.

Thanks Steve, after last winter, Ludlowii didn't sprout again :(, it had some buds, but in the end, the buds died off. So I thought it was killed by winter, it was very healthy last year. I am at 5b, but I did put Ludlowii indoor after late Dec. Anyway, it died in the second year:(.

I asked a question of Carol Adelman about planting tree peonies in pots, ordered a very short tree from them and was concerned about being able to see the blooms since it's a droopy bloom one (Alice Harding). She said it was the constant freezing and thawing that is the culprit rather than just the cold. Our winters here are bad that way, lots of snow followed by very mild temps and lots of sunshine. After her email response I decided to just plant Alice H near a 3' retaining wall rather than try the pot since I couldn't put a pot anywhere that it wouldn't freeze/thaw/repeat. Seems to work well for some gardeners if they're put in an unheated garage, too, don't have room in mine!