Starting an artichoke from seed?

I am having a great deal of difficulty getting artichokes started. I am attempting to start them in 6" pots to set out later this month. They are germinating alright, and growing fine until they have two true leaves...and then...flopping over and dying. I can't figure out why.

My first guess is that it is still too darn hot here. Some days are still reaching close to 100 degrees. I am starting them under the porch of our garden shed where they are shaded all day except for about an hour in the evening. For a while I thought maybe they aren't getting enough sun, so moved them into a vacant planting bed and put a row cover over them to partially shade them...and I think the heat and sun may have been too much. So I moved them back into the shaded area and they still seem to not want to get past the two true leaf stage.

[edit 9/14/09- I believe this heat issue is right. Artichokes need to be established, apparently, in temperatures below 85 degrees]

My next guess was the mix I was starting them in. I blended potting soil, homemade compost, purchased compost and purchased clayey topsoil. Maybe it was kind of heavy for the seedlings? Or, some of the compost is still too unfinished? Beats me.

I am having the best luck germinating the seeds in a hurry by placing them into a baggie on a wet paper towel and leaving them in the house until a few days after they germinate. It only takes about 5 or 6 days to get them to germinate this way. I am then transplanting into my potted mix. They seem to do fine for a week of so, and grow well initially, and then....death.