I've added this question to "gardening for beginners" to give it additional visibility.
I think the official word for the in ground storage is called heeling in, it might help you research more.
In my climate this is prime planting season for trees and perennials because they will focus on developing strong roots all winter long to better survive our harshest season. It may be completely reversed as far north as you sound.
The discussion in this thread https://permies.com/t/23257/move-young-apple-trees
may be relevant to you. I expect to see a more knowledgeable response after mine, but it's somewhere to start.