Q.Petunias grown from seed
Last year I collected seeds from my wave petunias.I have a small greenhouse so I germinated the seeds in hot beds.I got plenty of nice strong plant. The problem is the plant is all huge leaves. Really leaves larger than my hand. But no flowers at all. Just huge plants IV never seen any thing like this. Dose wave petunias have to be hybridized or can you directly collect the seeds.
Since Wave Petunia are a hybrid, the saved seed will most likely not be the same as the parent plant.
Many gardeners report the same, few flowers and small if any at all.
You could try an application of Phosphorous in the form of Bone Meal to encourage flowering. I would give it a try to see the outcome on these healthy looking plants.