OMGosh, I'm gonna follow this thread. I've been HEAVY studying my gardening books this winter. I discovered that onions can keep growing anywhere that the temperature doesn't drop below 20 degrees F.
I also found out that when you buy onion sets, you need to be picky.
The biggest ones are guaranteed to go to seed before they get big bulbs.
The littles ones will bulb nicely, but take F O R E V E R.
You want onion sets that are between 3/8in nad 3/4in, in diameter.
I've saved onion seeds before, but didn't do it last year
Wow I cannot imagine an acre of onion seedlings. I sow mine in a window box, sprinkle soil over top and water down and it goes under my light. I can't get Candy Onion Sets around here and they are expensive to buy and have shipped (I have done it from Dixondale but realized much cheaper to do it myself). Good to know about trimming them down, mine on my shelving unit are all up in the lights and no more room to raise the light. They are small when I set them out - some were no bigger than a cofffee stir stick - but in fall I have nice HUGE round candy onions that I pull, cure and they keep way up into the winter before I use them all up. I am also growing some spanish onions too. They were pretty easy to start and just look like little blades of grass coming up. I just let them grow, stick out in the green house usually sometimes in March or April and then plant out.
When growing main-crop onions from seed, the secret is in the preparation. To begin with you need a sunny site with good drainage but the key is to grow them in a permanent bed in order to build up the soil fertility. There is a down side to this however as you can also encourage the build up of diseases. With that in mind it's advisable to periodically rotate your onion bed with the rest of the vegetable garden.
If you soil is too acidic below pH 5.5 you will need to add lime to it according to manufactures recommendations. In general, onions prefer a pH of between 6 and 7.5.
It's possible to grow good onions on heavy soil, but you must improve the drainage first before planting. Add plenty of horticultural grit and bulky organic matter to the soil and then create a ridge of soil 4 inches high to further reduce soil moisture.