by Sadge, at Firesign Farm
The harvest continues. Granted, growing and storing your own onions isn't something everyone will want to do, but this is how I do it. When the first of my mature onion plants started to flop over a couple of weeks ago, I pulled the soaker hose off and bent down the rest. This gives notice to the onions that it's time to transfer all energy from the leaves down into their bulbs, and as the soil dries out the outer-most layers will start to toughen.
Next step is to dig up the plants, leaving them out in the sun for a day to kill off the wiry roots, then move them onto screens under the shade of the trees until the tops dry out too. If, or when, autumn rains threaten, I move them inside the sun-warmed garage to keep them dry and to continue curing.
Not all onions store well. Sweet raw sandwich-type onions won't store at all, and red ones usually not for very long. You have to start with the pungent yellow or white varities specifically labeled as storage onions to have them last through the winter. The little bags of onion sets sold in the big-box stores in Spring usually aren't storage onions, but you can play with curing the mature ones to see how well they'll do under your storage conditions. I like Copra onions when I can get them (my local garden store sells onion plants by the bunch in late winter), but this year had to go with Big Daddy so will see how they compare. If necessary, I might have to go back to raising my own storage onions from seed to get the kind I want.
I pick out the thick-necked onions and ones that formed a flower stalk (they won't dry well enough to store), damaged ones, and the ones that didn't form a nice bulb, and bring them into the house to use now for canning tomato sauce and salsa. The rest will cure in the warm airy garage, the longer the better, until the the leaves crumble off at the neck and outer skins rattle, so they'll keep in storage.
Onions store best in a cool (but not freezing) and dry spot. They can be braided, the same as garlic when the stems are still flexible, but I've found the stem often won't hold the weight of the bulb and an onion falls and bruises. They can also be stored in net bags, like I do my shallots (I reuse the net stocking-like bags oranges are sold in at Christmas-time for shallots - hanging them from a ceiling hook in my pantry), but it's harder to pull out ones that are starting to soften early enough to prevent them from spoiling the others. Some folks recommend using old pantyhose, dropping an onion into the toe, tying a knot, add another onion, knot, and repeat until both legs are full and hang the whole thing up. That's a bit too labor-intensive for my tastes.
I just store my cured onions in open shallow baskets down near the floor in my cellar, the coolest spot. That way, it's easy to sort through each winter week and bring up the ones that need to be used up first. My onions usually last at least until April, when I can then start on the first of the perennial Spring onions coming up out in the garden.