Lobelia likes moisture, and they don't like very hot weather. I have to say I'm surprised to see full sun.
Where are you planning on putting them?
I had them as spillers in my containers a couple years ago in full sun and every one died by mid July, and I live in NY, so it's not blistering hot here. If I let the pot dry out once... that was it, they were not coming back. Other plants would wilt then bounce back, but these babies crisped up like nobodies business. Last year I had them in hanging baskets on the north side of the house and they did much better, but they weren't prolific bloomers once July came around.
I kind of think of these as cool weather early blooming fillers, almost like pansy and snapdragon, while you wait for the summer annuals to ramp up. For me they did better out of direct sun. I would definitely give them some afternoon shade for the hottest parts of the day.
