They don't look good at all. They should be bright green. It might be your soil or fertilizer (what are you using?) or maybe they've been cooked on the heating mat. Petunias like it cool.

You still have time to start over in your zone.

I have had a few things, including one type of petunias, react really badly to the starting mix I tried this year. It was a really fine coir based mix. It holds water a long time, so it is easy to over water the little guys. It seems to be especially bad for slow growing seedlings that dont get transplanted out of it early. Most of my petunias did fine but there was one type Ultra Burgandy - that yellowed and stunted and mostly died.

If you try them again mix a lot of pearlite into your mix - it cant hurt.

You have several things working against you and the first one is the BioDome cells, the sponges. The primary reason why many recommend replacing them with a good potting mix instead.

Then there was apparently far too long on the heat pad. They come off the heat at the first signs of germination.

Then, because those cells stay so wet you are over-watering. Thus the yellow leaves.

Plus they are difficult to transplant. You can probably save some of these by transplanting them into a good quality soil-less potting mix. Unfortunately that means you have to plant them sponge plug and all so watering will still need to be monitored carefully. Once placed in potting mix those sponge plugs seem to go from sopping wet to bone dry and back to sopping wet. There seems to be no way to keep the soil moisture consistent.

Dave

I am very grateful for your timely replies and your experienced insights. I will transplant immediately. I have only fertilized once with a dilute PHC Plant Health Care for Seedlings and Houseplants from Gardeners Supply.

Luckily I have another batch of petunias and salvias that were started two weeks before these and are doing well.

Beth