I know that Walla Wallas don't store well and that onions will seed the second year. If I want to harvest Walla Walla seeds, do I just leave the onions in the ground? Will they make it to year two? How do we harvest seeds from Walla Wallas?
I don't know how winter hardy Walla Walla onions are in your location. I'd recommend leaving them in the ground. If they are larger than a golf-ball going into winter, then I'd expect them to flower the next year. If you want to hedge your bets, you could try storing some indoors, but that seems kinda iffy for Walla Walla.
Harvest seeds when the seed pods start to dry down. I harvest them, and toss them into an open bucket and allow them to continue maturing. At my place, grasshoppers are voracious predators of onion seed, therefore, I tend to harvest about the time that the grasshoppers start eating the seeds, even if that seems a bit immature. If I see any black seeds in the head, that's plenty mature. Once the pods are dry, I crush them between gloved hands, sieve them, then winnow.
How long are you looking to store them?
My Walla wallas are still doing well in the cold room.
Although some are trying to sprout a bit. But I didn’t get them cured down as well as they should have been so I think that is why they are green topped now.
Last year we ate the last just before Christmas so this year I will be able to see just how long they last.
I am in zone 3 at 3800 foot elevation and they have over wintered here okay. But we get a lot of snow so they are insulated.
I will be planting some for seed this year as I am very happy with how hey have stored for me.