Chop and dehydrate them. They will store indefinitely in a mason jar when dried and have unlimited uses. You can also slice and pickle them (couple of discussions on doing this here right now).

Bundling and hanging in a cool, dry, dark environment will keep them for a while but how long all depends on the variety. In time they will sprout and then rot, sweet varieties within a month, storage varieties within a couple of months.

So if you don't want to dehydrate or pickle them then freezing them chopped and in measured portions is the best option.

Dave

You can also carmelize them first (crockpot works well), then freeze. Reduces the space needed a bit.

Deanna

If you have a CrockPot / Slow Cooker, I 2nd the caramelizing idea.

We (GF & I) do a few batches every year. They come in really handy for beef dishes, soups, on sandwiches and burgers, canapes etc. etc.

See link below for a recipe. We use the suggestion of one reviewer and sub chicken broth for the butter. They turn out great either way.

Here is a link that might be useful: Caramelized Onions

So, after dehydrating or doing the carmelizing method, how do you freeze them?
I suppose the dehydrated ones could be frozen in a jar to be scooped out as needed, but how do you best freeze the carmelized ones? It seems like they would freeze in a big lump.
Do you freeze them in an ice tray, wrapped in waxed or plastic wrap or what is your best method???? Baggies seem rather wasteful. Nancy

I portion them into freezer containers and then Foodsaver the frozen blocks. We like onion soup a lot so I make soup size blocks.

Ditto jxbrown re freezing caramelized onions.

For dried, like spices, you don't have to freeze as long as you store in an air tight jar and store away from heat in a dark location. I have a Mason jar attachment for my FoodSaver so I vacuum seal my dried goods for that extra peace of mind... I'm nuts ;-)