I don't know what's wrong with the onions I planted last fall.
I never really thought about how onions grew until it started looking like mine weren't growing. I planted lots of onion sets in mid-October, well within the window for planting onions in the fall, or so I thought. Just recently, I started to wonder about those onions. They had pretty good tops on them, but when I pulled up a few, they hadn't bulbed - the bulb hadn't grown. So I decided I needed to do a little reading about onions. I found the following in The South Carolina Master Gardener Training Manual - "Short-day varieties, suited throughout South Carolina, begin to bulb when there are 10 to 12 hours of daylight." So, if onions for our area bulb when there is 10-12 hours of daylight, then the time frame for this is January 5th through March 21st in the spring and September 21 and December 3 in the fall. According to this information, onions in the fall need to planted well before mid-October.
(Just now, looking up the quote, I also read that lack of water could hinder bulb growth - so that could be my problem.)
As for planting onions in the spring, we're in that bulbing window now. I don't have mine in the ground yet - I've been too busy getting raised beds built and filled. I'll probably put out onions and potatoes in the next week. And I'm definitely going to need my landscaped beds as well - for all the potatoes and onions I have and all the summer crops I want to plant.