Put them on the compost heap

I often leave one or two plants to set seed. I have also dead headed them and got a later smaller flush of flowers. in a mild winter the may also survive the winter. if not copost them.

Allow the plants, to set seed, then collect most of the seed pods and store them in a paper bag, until the pods open and the tiny seeds fall out, then share the seeds out, with friends, family and neighbors.
Leave the plants with some seed pods, so they can self seed.