A couple pics would most certainly help as well as more details. Then someone may be able to chime in and help you.

SCG

Tucson, are you using the same techniques that you used in the past with success? If not, what's different?

Do you germinate the seeds in a flat and then transplant.....or sow directly into the peat pots, etc.? What's your fertilizing schedule?

Let's get to the bottom of this.

Do you normally remove your flats/pots from the heat mats right after germination?

I can't say this will fix the issue you are having, but the lights should be a little closer to the plants. Assuming you are using florescent tubes or CFLs, most people would recommend that the plant be placed 1 to 2 inches from the light, which has worked well in my experience also.

Failed to thrive is a bit vague, though. Do your plants continue to grow, just very slowly? Or do they end up dying after the leaves finally emerge?

Thanks for the replies. Sorry I can't do pictures at the moment, but to answer the questions: Seeds are started directly in the peat pots or 4" pots; the pots are left on the heat pad (the pad itself runs about 80°); I don't do any fertilizing until true leaves are well established. "Failure to thrive": The seeds will germinate appropriately, but true leaves take longer than expected (like, forever in some cases) and then growth nearly stops. Some just die. Peppers seem to do somewhat better than broccoli, tomatoes and eggplant (this year's starts). I've dropped the light closer to the plants, but it is too early to get results.

I'd remove the seedlings from heat mat and see if there's an improvement. Normally mats are used just for germination, media temps can get too high for root growth.

Definitely remove the heat pad once those seeds germinate, like dave said. If you start more seeds, have the light as close as possible to pots as soon as you see green seedling emerge from the soil. If you can't move the lights down, try stacking books or plastic containers to move the pots up towards the light. Hope that helps. Good luck!

Done and done! Impaired root development is certainly consistent with what I'm seeing "up top". Thank you all for your help. Hopefully, this will be continued at the dinner table this spring.