I tried growing big onions for 30 years, never getting anything bigger than a golf ball. We don’t have a garden anymore so it’s pots that used to be around the pool that disappeared Easter weekend.The key to big onions is variety and planting date. I would recommend an intermediate variety and planting late February or early March for your area. I've always gotten bigger onions planting in ground vs container. View attachment 388469
These got in late March, so I knew it was late. A variety I never heard of so took a shot at the pots. If nothing else, end up with green onions. I did a deep dive on YouTube and discovered they are heavy feeders so started putting a pinch of miracle grow around each bulb weekly before the rains. That really got the bulbs growing nicely.