The standard rules for storing onions are to store them in a cool dark place and to provide good ventilation. Well stored, they will keep for a good long time. It’s just the onions you buy in the early spring that start sprouting little green leaves – they’ve been in storage for a while and are anxious to find some dirt and begin growing.
But Riverview tends to send us sweet onions which don’t keep as long as storage onions. If I’m correct, our onions are sweet onions, relatives of the Vidalia but can’t be called Vidalias because we don’t live in that part of Georgia.
I keep my onions on a 2-foot diameter wire tray. It has little feet that keep air circulating underneath and the wire provides lots of ventilation around the onions. I try to space the onions out so there’s as little touching as possible. That just keeps a rotting onion here or there from hastening decay in its neighbors.
Some folks hang up their onions in mesh bags, like the ones that onions in the grocery store come packed in. Others swear by dropping an onion down the leg of panty hose, knotting it, dropping in another onion and repeating the process. Then you just cut off the onion/onions you need and the rest are separated. I don’t know about you, but I gave up on panty hose a while back so that’s not a storage method you’ll see at my house.
Whatever you do, it’s important to check the onions every few days. Take out the ones that are getting soft and cut them up, using the parts that are still good.
Do you have a dehydrator? Onions dry really well and reconstitute easily. If you don’t have a dehydrator, go ahead and slice up your onions and arrange them on a cooling rack suspended over a rimmed baking sheet. Turn on the oven to about 150 (or even lower like 125 or 100 if you can) and dry the onions there. The lower the heat, obviously the longer they’ll need to dry, but that lessens the chance you’ll turn them into burnt onions.
You can also freeze onions if you puree them first. You can freeze them in ice cube trays so you can pop them out and put them in a freezer bag, just retrieving as many cubes as you need. I wouldn’t freeze whole onions, but I understand it can be done. You can also freeze chopped onions, but don’t expect them to be crisp when they’re thawed. They’ll work perfectly, though, in any recipe where you’re sautéing the onions first.
Any frozen onions are going to be best used within a month, but they’ll keep for several months. Just don’t leave them in the freezer for a year.
Green onions: I just don’t know any great ways to preserve green onions except dehydration (yes, you can dehydrate them and chop into small pieces for adding to all kinds of wonderful things) so I just try to use them up. I rinse them and refrigerate and then chop them into all kinds of dishes that would call for bulb onions. I also love them in potato salad – which maybe the way we eat the most green onions (what does that say about my household?). I bake russet potatoes, then dice them peel and all and mix them with chopped green onions, sour cream, yogurt and salt and pepper. Could eat a whole bowl full right now.