It’s a little-known fact that many seasoned gardeners aren't aware of: you can grow onions (and shallots) in the winter. These super-hardy plants can survive incredibly cold temperatures with a little protection, and provide quality bulbs even after they bolt in the spring. As with most fall-planted crops, success is mostly a matter of timing.

Walla Wallas can be harvested green or just after bolting
Planting Fall Onions Prepare raised beds by incorporating compost, raking to create a smooth seedbed, then direct seeding onions about 1” apart in rows 6” apart in August or September. Once the onions reach scallion-size, harvest them individually with a knife until the remaining onions are spaced 3-4” apart. For Northern growers (those in Zone 6 and colder), mulching the plants with straw or leaves once they become established will help the plants survive the winter. In late fall, plants should be covered with low tunnels made of PVC or bent conduit and a layer of 6mil plastic sheeting. A layer of floating row cover placed over the plants in fall will improve the microclimate even more, resulting in an air temperature inside the tunnels averaging about 20 degrees warmer than outside. Growers in warmer regions such as the South and Pacific Northwest will often need to provide some type of protection for overwintered onions, but usually low tunnels, row cover or mulch is sufficient.

Small bulbs can be harvested in late spring
The Spring Harvest In spring you’ll find that the plants haven’t grown much over the winter, but with any luck most have survived. They will be about the size of large scallions in April, producing small bulbs by May, and generally are full grown (often very large in mild climates) by June. Many of the survivors will be sending up a scape to produce seeds, since onions are biennials—harvest the onions before or as soon as you see a scape appear, before it becomes large and starts to affect bulb quality. Just remember that these overwintered alliums won’t store very long – they should be used up quickly, just like a scallion or fresh market onion.

Bandit Leeks are a great selection for overwintering
Variety Selection Northern growers have fewer varieties to choose from that will successfully survive and form spring onions. They will be best served by intermediate or day neutral onions such as Valencia or Talon F1, Bandit Leeks and bunching onions like Red Baron and Evergreen Hardy White. Growers in warmer regions can grow these as well, and are more likely to have success with large sweet onions traditionally grown in winter, like Ailsa Craig and Walla Walla. Additional Resources