Question
why do petunias get sticky feeling?

Answer
Petunias exude a naturally stick substance through their stems that also spread to the flowers.  Although no one know for sure why this phenomenon occurs in only petunias, many botanists believe it is a defense mechanism to to trap sucking insects such as aphids and thrips.  Petunias are susceptible to these particular insects, so this theory is as good as any others I've heard.

Many gardeners find the sticky substance to be a nuisance and therefore do not grow petunias for this reason.  Breeders are working on new hybrid varieties that will not have this "problem".  But if this is indeed a natural process to ward of insects, the new hybrids may result in more a more sticky problem (excuse the pun) than the one petunia growers currently have.

I hope this answered your question.  Please write again if I can ever be of assistance.

Regards,

Mike