Curing is a month-long process of drying down your onions to prep them for storage. Once properly cured, onions will store for a very long time.
When your onions are growing, their stems are succulent and green.
When your onions have finished growing, you’ll notice the lowest stems start to yellow and wilt. Soon after, the green stems will flop over at the neck. You want to wait for most of your crop to flop over as well before digging up your onions.
Carefully pull each onion out by the bulb, or by digging around it. Pulling the weakened stem could cause it to pull off entirely, and you want the stem intact to reduce the likelihood of mold. Later you will lay the onions out on the ground, or in another open, sunny area, for a day or two to dry out the roots.
Next move your onions into a shady spot so they can start their month long curing cycle. You don’t need to clean off the onions until after they are cured. (I strung my onions out to dry on a clothes line. I then left them there for 4-weeks. Downside of not laying them out is your stems will completely dry out and you might have a few of your onions fall off the clothes line due to their wilted, dried out stems.)
Over the next 3-4 weeks as the onions are curing, their necks will gradually wither and the papery skins will tighten around the bulbs. Once the necks are completely tight and dry, and the stems contain no moisture, you can use scissors to trim the roots off the bottom of each bulb if you so choose. I just left the roots on.
Next you want to place your onions in a well-ventilated space like a brown paper bag, mesh bag, milk crate, a rack, or any kind of storage shelf.
Remember that even after curing, onions are still alive and really need a cool, dry place to stay dormant. If there is any change in temperature or humidity, it will cause the onions to break dormancy and start sprouting stems again. So you need to check your onions every few weeks for green shoots that might emerge in storage. If you have onions that sprouted, you will need to use up those onions first.
Enjoy your onions!