每日吃瓜

Putting it in the ground will thicken the trunk up. What you should do depends on what you want. If you are happy with the trunk the thickness it has, then you don't need to put it in the ground. We should always add to any advice, "But, it's your tree."
If it came from Brussel's it probably is not a breed native to Ohio, so you probably need to help the tree some. Probably you should put it in an unheated room that doesn't get much below freezing for the winter. I would think 20F for a couple of months would be fine, but it depends some on the specific breed.

pomegranate has many different breeds. Some are OK with frost, some are not. I would contact the seller and ask them their recommendation. Probably they would say, frost-free for winter.

What winter wheather you do get?

Planting in the ground in spring and moving it to a pot in fall would work. It will be slower than keeping it in the ground (But dead trees to not grow at all!) but faster than keeping it in a pot all the time.

Consider using a growing out box, a very large flattish container. I see good growth in these too, and these can be moved around.

Winters vary here but almost always get snow and temps to 0 and negatives with wind chills.

Maybe I will try leaving 1 in a pot and plant the other spring to fall (hoping I can keep them both alive!).

If that is 0C no problem. If that is 0 F you might need to do some protection.

Yeah that is F, I forgot to not that. If they both survive the year I think I will do spring to fall in the ground for one.

Thanks for all the pointers everyone.