Harvest: Pull up green onions as soon as they reach a usable size. For large or mature onions, you need to make preparations before the actual harvest. When the foliage of about half of all of the onions you’ve planted has yellowed and dried, push all of the foliage down to the ground. The onions will be ready to harvest about three weeks later, although you can leave them in the ground until you want to use them. Cut off any flower stalks that form.Once you’ve harvested the bulbs, set them out on newspaper in a dry, shaded spot a few days (for short-day onions) to up to three weeks. Then carefully clean off any dirt and remove almost all of the stems and roots and store in a dark, cool indoor space. Yellow onions generally are the best for storage.Harvest shallots when the shoots turn yellow and have died. Separate the bulbs and let them dry for about a month in a cool, dry, shaded space. They will keep for about eight months.More: How to Grow Cool-Season Vegetables