Hi there.

Petunias are annuals in zones lower than 10 and therefore in your zone which is 2B, it's an annual. Annuals cannot surive winter. These plants often have tropical backgrounds such as in the case of geraniums, balsams, So they die by winter.

The petunias you would have seen everywhere are grown from seeds in greenhouses and put out in the spring. So while it seemed they grew back, they were only started in greenhouses and brought out in springtime.

Ianna