Earthworm, Dixondale Farms is probably the best known supplier of onion plants. They have a good website with detailed planting instructions. See below. Good luck in getting those softball size onions.
John A

Here is a link that might be useful: Dixondale

Make sure you are growing varieties (long day, short day, etc) suitable for your zone. If you're in zone 8, you're probably too far south for big Walla Walla. I grow Candy and Superstar from Dixondale in zone 7 and get lots of softball sized onions. Must get them out early enough to develop good roots and leaves prior to bulbing and keep them well watered. Go to www.dixondalefarms.com and click on FAQ's and guides. If still have questions, give them a call - they are very helpful and, I think, Americas largest onion plant grower

One of the mistakes I made until recently was thinking of onions as another bulb and worrying about bone meal or some other source of P & K nutrients, when it seems bulb size is about # of leaf layers, so nitrogen is far more important. Good tilth sure doesn't hurt either.

john, although I am in z8 I am in Washington State where Walla Walla are from. I will try dixondale website. Thanks for the info all.

Dicot is correct, they are heavy nitrogen feeders. They also need plenty of room. If they get crowded they will stop growing. Keep the bed weeded and use a variety recommended for your area.

In WA you are in a perfect northern location to grow big Walla Wallas. Did you know that if started by seed they should be planted in September. That will give you large and sweet ones. If you want big ones I'd plant them 8" apart in the row with the rows 1' apart. You want to get as much green top growth on them before the days start getting shorter. My bet is that it's too late to grow giant one's this year. Last year I planted Big Daddy storage onions from Dixondale and got a good % of 5" bulbs. Harvested them in September and they are just now starting to sprout. Have fun! Tom

goatman so what you are saying is starts or bulbs of Walla Walla should be planted around here in September? Or is that from seed?

I grew acceptably large Candy and Copra onions in Portland, OR last year. I got transplants from Dixondale. They recommended shipping to my area on Feb 17, but also say that that extended sub-45 degree temperatures will make the plants think that their second year has arrived, and they'll bolt. Predictably, lots of mine did, way too many. So this year I'm planting the same varieties from seed. I don't have indoor grow-lights so I sprouted them indoors in a large tray and moved them to the cold frame as soon as they sprouted. That was early March and I've just now transplanted them into the garden. They are still way smaller than the Dixondale starts would have been back in February. But the bulk of their growing occurs in the later, warmer months, so I'm hopefull they'll size up. But I'm not betting the farm on it.

This year I didn't use Walla Walla sets I used some generic red and white bulbs to see what will happen for experience sake. I will either order from dixondale or grow my own from seeds next season. I think big onions are the most impressive above all other veggies (looks only not taste).

Earthworm- You'd plant seed in September and get some growth before winter. What you want to do is get as much top growth as you can before the summer solstice. After that the plants puts its energies into the bulb. The larger the top growth the larger the bulb. But even the small ugly ones taste good. Tom

I think dicot hit the key to large onions. Whatever you can do to grow more layers will give you bigger onions. Feeding with nitrogen will help. Setting plants out early will give them more time to grow more layers.

BTW, each leaf comes from one layer. So the more leaves equals more layers.

Also BTW, "sets" and "plants" are not the same. Plants are just that, young plants. Sets are bulbs which went into dormancy at a small size. The biggest onions are grown from plants.

Jim

So... could I grow long-day, storage onions in western Oregon's mild-winter maritime climate by planting in July? August? September? With the hope of harvesting the following season. With little bolting?

My onions are certainly growing enthusiastically right now. It's my first attempt, and I'm hoping for some big ones, too.

Dixondale sent far more onion plants than I expected to receive, and I had to crowd them into four containers, half as deep as I'd planned on, since I had to cut them in two. These plants were set into the containers on March 7, and I'm gradually pulling the ones I set close together for spring onions. Today my other seedlings are hanging out on the deck with the onions as they get hardened off. The onions look a bit ragged or leaning every which way to me, though they aren't ready, of course. They were pummeled with hail about a week ago, and that's why some of the leaves are leaning. I'm keeping my fingers crossed about them.

Those are self-watering 5-gal. buckets behind them with some new lettuce in four of them.

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I've seen some huge Walla Wallas here in Western WA. Not sure if they were late summer/fall sown or not. The main things to do to get big onions are:
1) Make sure you have 8 hours minimum of direct sun
2) space plants closer to the maximum spacing than the average or minimum spacing
3) Make sure you plant at the proper time. Seedlings in Western WA should probably go out between mid March and mid/late April depending on your microclimate. Plat too late and you will get small bulbs.
4) Make sure you have good soil fertility and fertilize well when they are young.
5) Keep the water consistent, while young especially, and really give it to them the moment the base of the stem begins to swell and bulb up.

Following these steps should work. As someone else said even the small ones taste good!

tc, I plant my storage onion plants, Copra and Big Daddy, in late March. The Big Daddy's get huge. What I mean as storage onions are ones harvested in September/October and still in good eating shape right now. Tom

earthworm,

The reason your onions weren't very big last year is you grew from onion sets. Sets never get anywhere as large as transplants started from seed.

You want a long day or day neutral onion in Washington State. Short day onions are for the southern latitudes.

For huge red onions I've had great success with Mars. I start the seed the end of March and transplant them the 3rd week of May. My plants are thinner than a pencil when set out, but by the end of August the bulbs are almost the size of a softball.

Last year I grew from starts (live plants) and they bolted at about mid July. The biggest I had was the size of a baseball.

I'm attempting good sized (Texas sweet) onions in containers this year...lol...wish me luck. The containers are huge, but still...they're onions! :)