I have a few seedling trees and the past two years we had a light and brief frost but the cold weather didn’t kill my abiu, I have noticed they will get chlorotic and they start weakening, I give them foliar iron and blue bag of hollytone (has sulfur) and they green up again. Have noticed they are way more actively growing during warmer months. It’s possible if they are malnourished they will have a tougher time handling cold weather. I have a thick mulch layer of pine bark chunks on them and keep them well watered.
-Joe