I started my leeks 1-1-11 in a south window and have trimmed them one time.I would do the same if I was starting onions but I don't start onions any more I buy plants. I transplant one time in to the garden. onions and leeks go in the garden mid to last of April depending on the weather.They usally get snowed on a time or two and it dosen't seem to hurt them. GOOD LUCK TO YA!! YOPPER

Onion and leek can be started now if you want. I just started leeks under lights. Length of day seems to not affect them . Most long day storage onions need to be started the first two weeks of February for the best bulbing where I live at the 44th parallel. I plant them out In May not waiting for the last frost. but later than yopper. I trim the tops and use them like chives for soup and salad until they are transplanted. Never done shallots myself. ;)

Curt

Thanks Yopper and Curt. I bit the bullet and started the seeds Friday - today there are babies peeking out of the soil.

I used Gardener's Supply Germinating Mix (my favorite) mixed with compost and transplant mix for the onions and shallots as they will stay in the 128 plug flat until planting out. The leeks got pretty much the same and were planted in 4x6 fiber pots. I plan to move them to larger individual cells when they are big enough to handle.

I put the "pots/trays" in 1020 flats and covered with domes to keep moist and warm. The lights are as close as I can get them with the domes on. Once more of them have emerged, I will lift the dome on one side (I use short lengths of small dowels to hold dome open) to allow more air flow and remove when most have germinated. I also run a fan where I grow my seedlings.

I am growing long day onions-Red Long of Tropea, Giant Musselburgh and Primor French baby leeks, and Ambition shallots. I started varieties that I have tried from local farmstands and liked.

It's been about 5 weeks since I started the seeds. I had great germination and potted the seedlings up to bigger cell flats at 4 weeks from starting - part of this being an experiment/learning experience.

The Giant Musselburgh leeks and red onions are in 4" deep 50 cell flats. I don't know that the onions needed that but that is what I did. I planted the leeks deeper than they were - it is what we do at planting time so thought I would start that process now.

The shallots and baby leeks are in 72 cell plug flats. shallots planted as they were in the smaller cells and the leeks planted a bit deeper.

So far, they are all doing very well.

One thing I discovered that I didn't like was using the 4x6 pot to start the leeks. It was a pain to untangle all those roots. Next time, they all go in their own cells - better for me and them I would think.

definitely plant them at april 15, because onions are cool season plants, but just in case always grow extras and keep them indoors for another few weeks.

The stuff the OP is mentioned are COOL/COLD loving things.
If you want to get a head start, you can start them early indoors, otherwise, I would just plant the seeds where they belong, ie, garden.
That is how I do it. My leeks, onions are just doing great.
I have never planted shallots from seeds but I would think they are not different from onions and leeks.
Another think is that allium seeds germinate in cooler soil, no problem.