MPL,

Petunias can be propagated from cuttings. You might need to use a humidity dome for a week or so, until the cuttings have time to "strike" enough roots to support their leaf area. I take cuttings from my best zinnias each Fall and grow them inside under fluorescent lights during the Winter. That lets me pursue my zinnia hobby year-round.

I use Physan 20 to prevent bacterial rot while the zinnia cuttings are forming roots, a rooting hormone (every one I have tried works), and humidity domes.

ZM

ZM:

Yes. Forgot to mention that I have successfully kept other variegated Petunias over the Winter, under lights. They do indeed root quite easily. Often they will actually bloom under lights. I doubt any commercial nursery would want to go through all that trouble ...

MPL,

"I doubt any commercial nursery would want to go through all that trouble ..."

I think they might. Some of the commercial petunia strains are grown asexually, and even Plant Patented. Like, for instance, Supertunia. The Proven Winner petunias are grown asexually, and sold only as plants, and not as seeds. And many of the near relatives to the petunia, the Calibrachoa, are grown asexually and Plant Patented.

There is big money in successful ornamental plants, and some commercial nurseries are willing to go to some trouble for a share of it. I am personally not a big fan of any variegated ornamentals, but many people are.

ZM
(not associated with any product or vendor mentioned)