You'll know your onions are ready to pick when, like garlic, they lie down. There are a few different ways to store them.
For keeping indoors in your fridge or any cool, dry place, let cure outside in the sun for a few days. Then just trim the tops and wash off any dirt, you are good to go.
When I recently told Mandolin I had read not to store onions in the fridge, he just chuckled and shook his head.
We have been doing that for years with good success.
We freeze some of the onions that will just be used in soups or to can later in the fall in salsa. No preparation needed, just peel, chop, spread out on a foil lined sheet, freeze and store.
You can also to roast/dehydrate some of the fresh cut green tops. You can use a commercial dehydrator but for onions, an iron skillet will add flavor to the end product.
Very lightly oil and place on medium heat while you chop the onion tops as evenly as possible. Then place in the warm skillet and reduce the heat to the lowest setting possible. It will take a few hours until your onions are crisp to the touch. Store in any food grade container on your shelf.
Dried this way they add a mild and toasty flavor to your food, and a little color to boot.
There are still plenty of onions growing in the garden, yet the sight conjures memories of a fall day not too long from now and homemade Three Onion Soup.
No hurry though, it can wait 😉