how hardy the onions are...

[Tania]

I knew the onions are hardy (and they do recommend to plant Walla Walla in the fall here in PNW to overwinter...)

... however, I still was quite surprised to see these tiny onion transplants (that I started from seed and transplanted on Saturday) to survive 2 frosty nights in the row (30F and 26F). They looked totally frozen to me this morning (and I was torturing myself all day thinking 'why didn't I cover them last night???? ), and when I came home from work and checked them again they were healthy and seemed to be quite happy.

Impressive.

my question is - how early (before the last frost) can/should you really plant the onion transplants into the ground? Does that depend on their age/size? Are they affected in any way when they get a few frosts?

In the previous 2 years (I didn't grow onions from seeds before that) I transplanted onions after the frost (~1st week of April), and I didn't get large bulbs. I was under impression that the days got too long here and they started bulbing prematurely. This year I accidentally put them in a week earlier - I'll see what happens.

I grow Walla Walla, Candy F1, Copra F1, and Red Burgermaster F1 this year. Last year my fall planting of Walla Walla failed miserably (lost the battle to slugs... and excessive moisture during PNW winter)

Btw, any recommendations on how to 'feed' onions organically?