This is the time of year that onions grow and develop rapidly. Regular watering (if needed) and a light fertilization are helpful to maximize growth. Onions develop so that as much as 2/3 of the bulb remains out of the soil. There is normal and there is no need to cover the bulb with soil.
Some varieties of onions are nearing harvest time when the tops begin to fall over. Others may not be ready to harvest for about a month. You may wish to break over the tops that haven’t fallen to encourage drying of the neck. Allow a few days to pass and then dig the onions to insure they don’t sunburn. Temporarily store them in a dry, well-ventilated area for a week or two before cutting the tops to insure the necks are completely dry. Remove the foliage (or braid the leaves) and store in a cool, dry location. (Ward Upham)