I just love the look of boxwood or spruce poodles trees (2 or 3 ball ornamentals) planted in urns. However, I've been told that they will not overwinter well in zone 7 in my shed. Would it be possible to cut the bottom out of my fiberglass container and sink it a bit into the ground so the roots are actually growing into the ground? Would it survive the winter like this? Any suggestions would be great! Thanks!!!