Peggy, do I understand that you started some MG's from seed in the ground outside, and also started some indoors in potting soil and transplanted them outside? Or did you buy transplants?
Just guessing here, but the transplants might just have stronger root systems since potting medium is lighter and possibly was warmer than the soil outside. This might give them a head start, even allowing for transplant shock. (you must have done a great job of transplanting) If you bought the transplants, they might have been going a little longer than the seed started plants.
The other thing that can boost plants into blooming is a bit of stress. Maybe the transplanting was the little bit of stress those plants needed to get flowers starting. If you can stand to 'stress' the other plants by witholding water for a day or two, that might give them a kick. Let them dry out really well, but not wilt.
