Are they old seeds? Seeds from onions only last a year(2 max).

No need for a heat mat with them either. Also, 1/4" max on the depth.

Next time, try moistening the soil first(not wet), put in the seed tray, tamp the tray on the ground a few times, spread seeds, crumble 1/8" inch fine soil over the top, generously mist the top.
Then in the dome, with or without mat until you see emergence. Once emerged, put immediately under shoplights or CFL's lights 1" from top of leaves.

Good luck.

Kevin

You might be trying to keep the planted seeds too warm. I always place leeks and onions in a cooler room to germinate. I also hold all these seeds in a freezer since you might not even get good germination after 9 months of normal seed storage. Get seed from a reliable source and ask when the germination test was made if it isn't written on the pack.
I've had excellent results with Todorna and Jersey varieties. I dribble seed in slight indented rows (7/tray) in a 1020 tray and lightly cover with media (less than 1/8"). Like with onions, I give plants a "Haircut" a few times before they get transplanted. Mine are growing slow in rows in the garden, ~ 4" spacing between plants.

I treat leeks the same as onions, except that I bury them deeper each time they're potted on. Germination is just about 100% as long as my seed is under two years old. Try germinating without the heat mat as the previous posters have suggested, but also refrain from "fluffing up" the soil so much. Pre-moisten your starter medium and firm it into the pot. Firm the soil you cover it with, too. If the growing medium is too fluffy (has too many air pockets), it won't make good contact with the seed.

Agree: Alliums seeds get old fast. Also, germination time depends on soil temperature. Third: I always sow three times more seed than space permits. Then all I have to do is to thin. Some seeds won't germinate, not because they are old but have not been fully developed and viable when collected and then packaged.

Thanks all! Great stuff.

The seeds are brand new so I'm guessing the heat pad is the culprit.

How cold a temp can they take? Now that my A/C is running the basement is pretty chilly.

Thanks again!

I agree you do not need the heat mat and it could be the problem. I've had okay germination even on seed a few years old. I sowed heavily because of the older seed and now have LOTS of baby leeks, more than I have room to plant.

The seedlings take a long time to look like much, and I often think something is wrong with them. But after a month or so they look more like I think they should although they are still tiny.

This time of year I start leek seeds outdoors and grow them in crowded pots until I have the space to plant them, usually after early potatoes. I will start more seeds in a month or so for using as overwintering leeks. Just harvested the last of my 2012 leeks last week, leaving the plants that are actively multiplying by division. When replanted, the little plantlets that cluster around the mother leek grow into strong plants quickly.

Planatus, you just answered the question I was going to ask here... Before I even asked it! *cue slightly spooky music* You can be The Plant Psychic! Seriously, I was wondering if this would be the time to start them for fall and winter, so thanks, cheers!