Don't pinch off the spent bloom. Wait. After the trumpet falls off, there'll be a pyramid shaped seed cone left behind. Wait (some more!) till it turns brown. At this point (or just before) you can gently put a little bag over it to catch the seed, or a tray or pan underneath. Or you can pinch off that section, and put it in a container or paper bag (ya need good air circulation) to dry it out further. The pyramid cone should burst open on its own, or when it feels really dry & hard you can carefully poke a hole it in to shake out the seed. The seed is super tiny. But there's a decent amount of it in one pod.
I keep most of my seed in an unheated garage, out of the light. I usually store it in glass jars or old prescription bottles.
Thank you nedweenie :) I just got this petunia and I love it! I want to make sure I have it around for a long time :) I would be happy to send you some seeds when I successfully harvest them if you like.
This is the one I have http://davesgarden.com/guides/pf/go/124954/
You're welcome. Keep in mind though, that since it's a hybrid, the seed grown offspring won't be exact replicas of the parent plant. (Or unfortunately the seeds might even be sterile.) If you want that exact plant over & over, your best bet is to take cuttings and propagate more petunias that way.
I "overwinter" alot of tender annual cuttings in my basement under lights, but I've never done petunias. I read on another forum about someone who manages to keep their petunia plants going in cold frames over the winter, but their zone was zone 6. So I don't know how, or if, that would work in TX.
And thanks for the offer, but I have more saved seed than I can deal with myself! :)