Ah I think this is what I was reading... http://www.dixondalefarms.com/apr10

Some more advice here... http://www.seasonedhomemaker.com/growing-onions/

How big are your allium transplants grown from seed and what is the weather like when transplanting?

I guess if they get too big, you can make like Dixondale -- pull them out of the pot and induce a couple weeks of dormancy.

My onions are usually a little smaller than a pencil at the soil level when planted out. Dixondale's seedling bundles will usually be all over the map with some about the size of a toothpick and others larger than a pencil. I plant out onions and leeks in the last 10 days of March and usually protect with AG19 frost blankets for the first couple weeks depending on the forecast. In the past I have had some get killed if unprotected with lows below 23 or so. The leeks are pretty easy to protect from a hard freeze because they are down in a 4-6" deep trench.

Thanks LoneJack -- yes, that is a good point, you really sink the leeks in, and they would be very easy to protect.

Most commercial bunches have a variety of sizes involved, not just Dixondale. Mostly the smaller ones catch up, but I plant the real small ones tight for green onions. Once the frost is out up here, we seldom get down into the low 20's; so my early onions are seldom injured and don't get any special care. I plant by the weather and season rather than by size of the transplant. You want to plan ahead to be ready when the season is proper. Even if you plants are a little undersized for onions, it is better to get them in the ground outside at the proper time for your area; so they get the proper daylength exposure.

Here in zone 4 I start planting as soon as the ground is dry enough to handle and frost is out. That is around the second week in April these days. To get a jump I try to have the early beds prepared the previous fall; so I don't have to worry much about bed prep. Sometimes the window for garden work is very tiny between rain storms etc. A little advance prep just makes things go easier and quicker when the windows open up.BTW I have very little problem with bolting in my multipliers and my Copras. I even plant back small Copra bulbs for another season of growing on, and still have very little bolting. Same goes for when I used to plant onion sets, the key then seemed to be to plant real shallow, right at the surface. I got a few bolts buy mostly not.

Thank you, Peter for asking this question, and Thank you Lone Jack and OldDutch for the great answers! Onions are one of my favorite crops, and I appreciate knowing more about them. This post answered questions that I didn't even know I had to ask. My onion crop will be better this year for it!