Michigan State University Extension
Preserving Food Safely - 01600008
Harvest onion family crops when the tops have died or in the late fall before the ground freezes. Allow the plants to dry for several weeks before storage. Spread them out on on an open screen off the ground.
Do not try to store bruised or thick-necked bulbs. Storage should be in a dry, well-ventilated area with a temperature near 32 degrees Fahrenheit. Place the bulbs in mesh bags, fill bags half full, and hang them from overhead hooks in the storage area or place them in open slatted crates, half full, and stack crates on cross bars.
Slight freezing will not be harmful if the bulbs are not handled while they are frozen. When stored properly, the onion family bulbs should keep through the winter.