When repotting plants in containers, one is only supposed to go up a size, and not make a big jump in size. Why? Reading about hostas in containers, I find that a big jump in size will kill the plant. When planted in the ground you are planting it in a huge container.
What I learned is the most important thing to get a container hosta to winter over outside in the north is to keep rain off it when the soil is frozen.
Don.