Once an onion sends up the flower stalk (bolts) the bulb will quit growing and become hard, woody and hollow. If you catch them as the flower stalk emerges, they do ok as green onions. Clipping the bud as it emerges will slow the process some, but not to the point of getting good mature onions. For future refernce you will need to look closely at appropriate cultivars for your area as well as best planting times.