The article below written by Rachel Arsenault over on Grow A Good Life Blog, gives great details on how to grow onions but especially how to cure and store your onions.
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Try to harvest onions on an overcast day to reduce the sun damaging the bulbs. The easiest way to harvest a large amount of onions is to use a digging fork to carefully loosen the soil under the onions. Once the soil is loose, grasp around the neck of the onion stalk and pull them up gently trying not to tear the roots, stalks, or bruise the bulbs because damage will reduce the onion’s storage life.
If the sky remains cloudy, I like to spread out the onions on my garden fence so any soil that is still clinging to the bulbs can dry and be shaken of before bringing the onions inside to cure.
Curing Onions
Curing onions allows the outer layers to dry out and tighten forming a protective wrapping around the bulb. Onions cure best in a shaded, dry, and cool place. This can be in a shed or on a covered porch away from direct sunlight. Our summers are humid, so I usually bring the onions inside and spread them out on wire shelves in the basement where we run a dehumidifier to keep the moisture levels down.
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To read the full article go over to the Grow A Good Life Blog.