Onions need to remain dry after harvesting.
image by Sanja Gjenero/sxc.hu
Onions are actually edible bulbs. While you can harvest onions at any time, most gardeners wait until the bulbs have grown to their fullest potential to harvest the bulk of them. This harvest occurs in late summer, when onions are dried and cured so they can be used during the fall and winter months.
Harvest green onions when the plant (top) is about six inches tall. You can let them grow longer for a more potent green onion, if desired. Grab a hold of the top, near the soil and pull. You do not need to dry out green onions.
Wait until about 85% of the tops are fallen over for traditional onions. Then go ahead and bend over the rest.
Leave the onions in the ground for 10-to-14 days so they can mature.
Choose a sunny, dry day to harvest. This important since harvesting onions when it is rainy or humid can prevent proper drying.
Pull the onions out of the ground. Grab a hold of the tops close to the ground and yank them out.
Lay the onions out until evening time to dry. If it very sunny and bright out, move the onions to the shade to dry out so they don't burn. Move the onions to a dry area before evening so they don't get wet when dew forms.
Braid the top and hang them to dry for 2-3 weeks to completely dry them out and cure.