Texas is a big state and a major commercial producer of sweet onions, but like Georgia probably only grown in certains areas. Anyway onions are pretty easy, too many folks overthink the process. Short day onions are started from seed around Labor day and transplanted in December. I use grow mix in planting trays and start the process in a cooler shady spot. Strart moving them to more sunny locations as the weather cools. There are two key factors when transplanting. The onion is not a root crop. It is a leafy vegetable, the bulb is actually modiied leaves. They require N and water at corn levels. I use a high N fertilizer in soil prep and side dress again late March when they start bulbing. I can grow long day onions with some effort. The problem is protecting them from summer temps. They do not start bulbing until June and have to grow the triple digit temps of July -August. These are also commonly dry months so it is difficult to provide them enough water. Photo is a sweet Spanish Golden Grande, which I experimented with a couple of years ago. Nice onion, but occupied time and space that I could use for other things.
