You might want to post this in the seed starting forum as well.

Did you cover the seed? Lobelia needs light to germinate. It should just be sprinkled on top of the soil and gently pressed down to have contact with the soil. Lightly mist them every day to keep the seeds moist

The optimum temperature for germination is 65F to 75F or 18C to 24C so you might rethink the heat mat. They also take a long time to germinate--up to 3 weeks-- so be sure you are not giving up too soon.

I grow them every year in my greenhouse and have never had a problem with them. I keep it at around 10C at night and the sun heats it in the day.

I hope this helps

Thanks for your input! They were correctly sown (three+ weeks ago) & I had them in my germination chamber at 70F with light & adequate moisture....... Tried this same seed last fall with the same results....

I did look up germination for this variety and it does say they require a slightly higher germination temp-closer to 80 F. Maybe you need to raise it a bit and see what happens. The seed might be still layimg there dormant.

I have never grown that variety I usually grow cryatal palace white and dark blue and have no trouble with them

I answered in the Growing From Seed forum.

Art