You may not be doomed. I have volunteer petunias every year pop up where the seeds get thrown from plants. I plant petunias in patio pots and all along the patio more and more petunias pop up. My grandma never planted her petunia patch next to her kitchen door and each year it was a mass of petunias in a 8 X 8 area - she was in northern MN zone 3.

This is my first year WSing them. I particularly moved those container to a shaded area.