Last fall we did an experimental planting of garlic in boxes in our greenhouse.
We are able to overwinter this garlic in a greenhouse that is kept at about a minimum of -5 C.
It came through the winter beautifully and we moved the boxes out to our outside beds about 3 weeks ago. these beds have bottom heat are are covered if it is going to freeze at night. We left two boxes outside in an unheated uncovered location and they appear to be doing about the same as the ones pictured here.
In between the garlic patches you can see a crop of perennial winter green onions. They came through to winter looking very good as well but small. They are starting to pick up speed now. We would likely seed them much earlier next year in order to harvest green onions in March or April.