I would guess that the yellowing is from overwatering, that's generally what is happening with mine when they exhibit that symptom. Also, use 80-90 degree water - cold water can slow a heat-loving plant's growth. Other than that, I'm not sure what would cause the seedlings to stall for that long a period.

Give them some time. As dicot says, they are heat lovers, of warm soil and warm nights, not just some warm days. Even though we've had some warm weather off and on, they won't really get going until July--until the nights get above and stay above 60F.

More warm days and nights I agree will speed up the growth. The mix they are planted in sounds all wrong. You did not say if these are potted or in the ground but your mix is not appropriate for either. Al

Thanks for the help! I'll be waiting to see if they do something. I've got them in planters that I built. I'm trying out the square foot gardening thing this year, so that's why the soil mix is this way. Is there a better way soil wise?
-K

Yellowing of the foliage is often the result of soil that does not drain. Container soil should be composed of course material with large enough particle size that allows water to drain through and out the drain holes in the container. If the root zone remains saturated, oxygen will be excluded preventing the roots from taking up water and the nutrients dissolved in the water. Much good information on container soil composition is found in the container forum. Al