See this blog from Moongrower:
http://www.growsonyou.com/moon_grower/blog/17159-how-to-store-your-onions-over-winter-and-other-tips

There's a video of exactly how this is done. Look in Google.

Or use an old net or women's tights... I enjoy plating them as per Bulbs direction :-)

Oh gosh how this reminded me of the good-old-vegetable-growing days I used to know in Norfolk - er, the one in England! - (though I think it was then so long ago that we were recommended by the pundits, to store our onions in 'laddered stockings'...)

I came to Norfolk a really TOTAL gardening novice, thinking onions grew on bushes (like pasta!).... and then proudly learnt to grow them (when the birds didn't beat me to the sets) and to string them up in bunches underneath the eaves of the coalshed, in a sheltered place. Being able to use them in the Christmas sage and onion stuffing was for me as a young "housewife", a special pride, my first year of growing them! Ah dear dead days (here in France it's really not worth the space or the effort for me, the bought ones are good and cheap... and the available eaves are too high up!) But I do miss the achievement.

(By the way, if the stems are short a needle and thread to give the stalks some "hair extensions" before you plait them is a good trick - good old-fashioned darning thread, eh?! - you could at least see it, but who darns, nowadays! - but any strong thread would do).

Incidentally (a rant from an "oldster" (!) ) - while on the subject of onions, does it annoy anyone else when those 'TV chefs' demonstrate preparing onions by first stripping off several layers of flesh (from the onions!)... when with literally a moment or two more you can tease off just the papery stuff and keep more of the perfectly edible onion? I suppose if they grew them, they'd be more jealous of wasting them...