Puny Petunias- HELP!

Hi all!
Well I started my Parks Dolcissima Flambe Petunia's on 2/28. They we mostly all popped up by 3/11, but now, they have completely STALLED in the last 2 weeks. Now I ended up started one 6pak in Miracle Grow seed starter and the rest in Jiffy Organic, and although I did not like the Miracle Grow for its texture (way too many bumps and chunks) and I did like the nice fluffy smooth Jiffy- the ones in Miracle Grow are markedly bigger.... but even then, they have not changed much in the last two weeks either. They are all moist, and on a heat mat with light very close.... It seems like they need something? Maybe fish emulsion in the water? Any suggestions are welcome..... I thought Petunias were easier..

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I would definitely take them off the heat mat now that they've sprouted. The soil temp might be getting too warm. They shouldn't need fertilizers yet since all of they're nutritional needs were met inside of the seed.

Thanks CindyMzone5 I took them off the heat. I was glad to since I needed the heated space for more stuff anyway. Hopefully they start to "go" soon.

How much sunlight are they receiving?

Are your grow lights fairly new? I know I tend to be frugal and use the same light tubes every year (shame on me!) but the lights do tend to lose lumens over time.

I was going to suggest some strong sunlight but perhaps the grow lights are the only available source of light?