It was cloudy all day today, but I'm not complaining as Mother Nature has mid 50's and sunshine for the weekend for us here in south central Illinois! Woohoo! Yep, sunshine can make a cool weather day very nice. And, if no wind it's even better! I don't mind 40's and 30's and even 20's when there is sunshine and no wind. But, that wind BITES!
Fishy, Addy answered your question very well, Just plant the pot and all for the tree that you need to bring in dirt. By leaving it in the pot, the roots will grow less, which is fine, as they will be dormant, as Addy pointed out. Just don't want the roots to get more frozen above ground than they would get under ground. Typically my ground here only freezes the top few inches, so as long as you put them down the depth of the pot, they should be fine. I think landscapers in this area pile mulch on the pots of trees they overwinter to help insulate them. Then, come spring, when the plants start growing, you can dig them up and place them where you want them. In my case, I had so many plants that I replanted them for 2 years! It was quite fun, actually. Kind of like having my own landscaping place. LOL