Scroll down for dianthus. They're easy to see, once they begin to form.

Here is a link that might be useful: The Seed Site

I just tried to collect some of these yesterday. And realised I had picked too early. I did have some swollen buds with immature seeds so know where to look for them now. Maybe you can pick a seed head or two and look and maybe find where they will grow too. The longer the flower has been dead the more likely you'll be able to find this.

I picked the whole dead flower head off... carefully pulled away the petels of the dead flower. Inside of those petels you should see a swollen pod (mine were still green cause they were not ripe seeds...when ripe they should be brown). If yours are not ripe like mine were not you may be able to see the immature seeds still though for future reference. Open up that pod and you will see clearish/white itty bitty tiny balls (look hard!) those were the immature seeds. Now I know to wait longer and check on progress of the plant till I find the seeds are dark one day.

I collected seed from mine last fall.Once the flowers have dried right up to little brown sticks the seed just pours right out in your hand.I have planted some for plants for next year and they all germinated well.

I just collected a bunch of these from my grandmothers garden today. When the flowers are dried up and turn brown, just pick them off, put them in a ziploc bag, and shake. They'll fall right out. Then I pour them into a strainer with a bowl underneath and all of the chaff stays in the strainer while the seeds fall into the bowl. Easy!

Thank you all. Now, if I can just keep my Dianthus alive during this dought/heatwave....