After several years of research, we know that it is possible to plant bulbing onion (Allium cepa) in the fall, overwinter them in low tunnels, and harvest bulbs by late May in Durham, NH. For detailed information about this system, see Research Report: Overwintering Onions 2014-15. In response to grower inquiries, we expanded this work to look at non-bulbing onions, also known as green onion or scallion (Allium fistulosum).
Our objective was to compare overwinter survival of several scallion varieties planted at three different fall planting dates. Access the full report for more details.